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  • The Return of Swamp Metalmarks

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    Tags: conservation, swamp metalmark, Peggy Notebaert Nature Museum, butterflies, Biology

    Created: 6/27/2013      Updated: 8/9/2016

    After the very challenging drought year of 2012, the Butterfly Conservation Lab is up and running. Recently I traveled to far southern Indiana to continue our ongoing work with the Swamp Metalmark.

    Swamp metalmark habitat in southern Indiana.
    Swamp metalmark habitat in southern Indiana.

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    The swamp metalmark is an endangered species in Illinois.  In fact, many people consider it to be extirpated (locally extinct) from the entire state. The reason the butterfly is so rare is that it inhabits an extremely rare type of wetland called a fen. Its caterpillars can only feed on the leaves of swamp thistle and tall thistle. Both grow in fens. We are attempting to re-establish swamp metalmarks to their last known home in Illinois, Bluff Spring Fen near Elgin.

    Swamp Metalmark
    Swamp Metalmark


    In Indiana I found dozens of metalmarks from a wooded fen near the Ohio River. We brought four females into the laboratory, and set them up in special cages to lay eggs. Over the course of about a week and a half, the butterflies laid over 200 eggs. We are currently waiting for them to hatch. When they do, we will place them on leaves of swamp thistle and rear them to adulthood. We hope to have adults in August when we can release them at their new home. With a bit of luck, they will establish a new population.

    Egg laying cages with female metalmarks in them
    Egg laying cages with female metalmarks in them.

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    Doug Taron, Curator of Biology

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  • Carnivorous Plants of the Chicago Region

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    Tags: horticulture, Biology, carnivorous plants, plants, wetlands, bogs, marsh

    Created: 6/26/2013      Updated: 8/9/2016

    People often think of carnivorous plants as being tropical monstrosities, but many species make their homes in cold climates, and some can even be found in the Chicago region. The Museum's Biology Department took a trip several years ago to the Indiana Dunes' Pinhook Bog (open only to guided tours due to the fragility of the ecosystem) where we saw sundews, pitcher plants, and bladderworts--all species that make up for the low-nutrient peat moss they grow in by digesting insects. Combined with the rare orchids, blueberry-lined walkways, and the fact that the ground moves when you walk on it, it was one of my favorite daytrips. Volo Bog, north of Chicago, is home to such strange plants as well.

    Sarracenia purpurea
    Sarracenia purpurea

    While the Venus Flytrap (Dionaea muscipula) is the most iconic carnivorous plant outside of Super Mario Brothers and Little Shop of Horrors, our local meat-eating flora have plenty to offer. Pitcher plants (Sarracenia purpurea) have leaves that form a tube that collects rainwater. The attractive red coloration draws curious creatures to the rim of the "pitcher." Occasionally an insect will fall down the slippery slopes into the pool of rainwater and be trapped, and shortly thereafter digested. But since plants lack teeth, the plant has to hire someone else to chew its food. It is said that "If you build it, they will come," and a host of invertebrates make their home in the water of the pitcher plant, forming a mini-ecosystem inside the leaves of one plant. The top predator is usually the larva of the Pitcher Plant Mosquito (Wyeomyia smithii), one of several animals which lives only inside pitcher plant puddles, and nowhere else. Please don't think we should fog the bogs, though; the pitcher plant mosquito doesn't go for people. Eventually bits of the prey are chewed, shredded, digested, and excreted by enough little bugs, bacteria, and other critters that nutrients from the victim's body become usable by the plant.

    Sarracenia purpurea
    Sarracenia purpurea

    Drosera rotundifolia, the Downy Sundew, takes a different tactic. Its leaves are covered with red, tentacle-like protrusions, and coated in a sticky, sugary substance.  When prey come investigating they get stuck. The tentacles then curl up around the insect, and the plant begins to exude enzymes to extract precious, nitrogen-containing compounds that are otherwise hard to come by in the sundew’s habitat.  This is because in bogs, the high acidity of the peat moss and water inhibit the breakdown of organic matter, so nutrients remain locked away instead of cycling through the ecosystem as they might in more garden-variety soils. Many Drosera species have become so adapted to their conditions that they completely lack the enzyme that enables other plants to absorb nitrogen from their roots.

    Drosera rotundifolia
    Drosera rotundifolia

    While our collection is small, the Museum does maintain several living examples of carnivorous plants in our Mysteries of the Marsh exhibit. As these are wetland plants, they are members of some of the most imperiled ecosystems in our region, and throughout the world. While we are tempted to think of plants as basically immobile, passive denizens of our world, carnivorous plants are some of the most obvious examples of the incredibly active role plants take in nature. Stop by and see ours, but more importantly make sure to get out into the wild, visit our protected wetlands, and spot these fantastic plants in their native environments. You won't regret it.

    Andrew Wunschel
    Assistant Horticulturist

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  • Collecting Our Living Collection

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    Tags: living collections, Biology, Peggy Notebaert Nature Museum, crayfish, minnows, field work

    Created: 6/26/2013      Updated: 8/9/2016

    It's a question I get asked all the time, ‘where do you get your animals from?’ There is no short answer, some are donated, some are left at our door, some are purchased, some are bred in house and some we go out and collect. For this last group we can’t just go out randomly picking up any animal we like the look of, as a scientific institution we have to have all the appropriate paperwork and permits to allow us to collect our specimens. Also we are collecting creatures for live display so we have to be very mindful of our collection methods.

    This past week we were out collecting fish for our tanks in the Riverworks exhibit. Last year when we did this we had very little water to work in because of the drought, this year we had the opposite problem!

    Biology team wading through a river

    Trying to use a seine net in rushing water is a bit of a challenge to say the least and for the species we were looking for we needed to find some quieter bodies of water. It took us a while but we eventually found some good spots.

    The seine net is held in place while a couple of people drive the fish forward into it.

    Biology team catching fish

    The net is then scooped up at the last moment to secure the fish in the middle of the net. This method ensures the fish are completely unharmed in the process and also allows us a good view of everything in the net.

    Biology team examining their haul

    You never know what you are going to find in the net, which is all part of the fun. This particular scoop had a number of huge Bullfrog tadpoles in it and also a rather startled looking frog in amongst the mud and weed. They all got safely returned to the water.

    Bull Frog tadpoles

    We were looking for compatible species to the ones we already have on display so this haul of Top Minnows were a great addition.

    Minnows

    Some of our cache is photographed and then returned to the river, like this beautiful Heelsplitter mussel.

    Heelsplitter mussel

    We also ‘do our bit’ collecting up invasive species. Well actually, one particular invasive species, the Rusty Crayfish. An extremely popular snack for our Blanding’s Turtles!

    Rusty Crayfish

    Inspite of the high water levels we had a very successful trip, bringing home lots of new fish which will undergo a 30 day quarantine period before going on display.

    Celeste Troon, Director of Living Collections

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  • The Atwood Celestial Sphere -- A Centennial Anniversary

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    Tags: Chicago Academy of Sciences, Atwood Celestial Sphere, Archives, education, astronomy, exhibits, science, history, planetarium

    Created: 6/21/2013      Updated: 8/9/2016

    In June 1913, the Chicago Academy of Sciences presented an exhibit to its visitors unlike any other.  It was a planetarium where, unlike others of the time period, visitors could walk inside to experience the night sky while the apparatus rotated around them.

    Atwood Celestial Sphere at the Academy’s Laflin Memorial Building

    Atwood Celestial Sphere at the Academy’s Laflin Memorial Building, c1926

    The Atwood Celestial Sphere was designed by and named for Wallace W. Atwood, who served on the Academy’s Board and briefly as Acting Director of the museum. Mr. LaVerne W. Noyes, President of the Board of Trustees, had the structure crafted by his company, Aermotor Windmill Company, and donated it to the Academy.

    Wallace W. Atwood inside the Atwood Celestial Sphere

    Wallace W. Atwood inside the Atwood Celestial Sphere

     

    Atwood Celestial Sphere

    Atwood Celestial Sphere, c1913

     

    The sphere, constructed of a thin galvanized sheet metal, was only 15 feet in diameter.  Tiny perforations in the exterior of the sphere allowed light to penetrate, appearing as stars to those viewing from the inside. Atwood designed the celestial sphere to portray the stellar sky as seen from Chicago and visitors would watch as the sun, moon, and stars rotated around them in simulation of Earth’s orbit through the solar system. The sphere was utilized heavily for educational programs at the Academy. School groups, clubs, and other visitors would tour the sphere, with programs often led by Atwood himself during his time with the Academy. 

    Wallace W. Atwood with children inside the Celestial Sphere

    Wallace W. Atwood with children inside the Celestial Sphere

     

    The stars were positioned with such mathematical precision that in 1941, the U.S. Navy began incorporating use of the Atwood Sphere in navigational training exercises for the U.S. Naval Reserve Unit stationed on the Chicago Campus of Northwestern University. Modifications were made to the Sphere to accommodate these trainings, including the installation of a meridian (an arc that follows the circumference of the sphere and passed through the zenith) and movable arm with which to measure the zenith angle – the distance between the zenith (the point directly overhead) and any star.

    Atwood Celestial Sphere at the Academy’s Laflin Memorial Building

    Atwood Celestial Sphere at the Academy’s Laflin Memorial Building, c1920s

     

    In the 1960s, the Academy began extensive redesign of its exhibits and developing life zone dioramas created by William Beecher and Academy staff. The exterior of the Atwood Celestial Sphere was painted to look like the Earth and the ceiling of the Laflin Building painted to look like the night sky to blend more readily with the new exhibits.

    Thurston Wright working on the Atwood Celestial Sphere

    Thurston Wright working on the Atwood Celestial Sphere, c1950s

     

    Atwood Celestial Sphere with the exterior painted to look like Earth

    Atwood Celestial Sphere with the exterior painted to look like Earth, c1960s. William Beecher in the foreground and Thurston Wright in the background.

     

    The Atwood Celestial Sphere was transferred to the Adler Planetarium in 1995 when the Academy vacated its Laflin Building, where it currently resides.

    Dawn Roberts
    Collections Manager

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  • Harriet the Spider

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    Tags: tarantula, living collections, Biology, arachnid, shedding, celebrity

    Created: 6/12/2013      Updated: 8/9/2016

    We are all rather fond of Harriet here at the Nature Museum. She is a very large, female Striped Knee Tarantula who has been with the institution longer than pretty much everyone. She has been here so long that I have never actually been able to find any record of where she came from or when. In spite of her somewhat intimidating appearance she is a very gentle creature and also quite a celebrity. She has featured on a blues album cover.

    Album cover for Eddie C Campell's "Spider Eating Preacher", featuring Harriet the tarantula



    She has done numerous TV appearances for various local stations and she also appeared on the cover of a medical paper about treating arachnophobia.

    PNAS Journal Cover



    But in between all this jet setting she is just a regular arachnid. She spends most of her time in the Istock family Look-in-Lab raising squeals from countless children.

    Once in a while we will notice that she starts to slowly spin a thick web mat and then we know exactly what she is up to. She is getting ready to shed.

    The first time she did this after I started working here I was alone in the lab one evening, I have to confess I had never seen a tarantula shed before so imagine my horror when I walked past her tank and she was laying upside down with all her legs in the air! Absolutely no prizes for guessing what I thought. I was so upset and spent most of that night imagining having to tell everyone that dear, sweet Harriet was no more. When I came in the next morning there appeared to be TWO tarantulas in Harriets’ cage, and they were both the right way up. By now I had begun to put two and two together, or in this case, one and one and realized what had happened, Harriet had shed. I have been here for several years now and after the trauma of that first time I made a little sign which reads ‘She’s not dead, she’s shedding!’ I have witnessed numerous Harriet sheds and each time I marvel at the process. Here is Harriet the morning after her most recent shed.

    Harriet with recent shed



    She is the one on the right of the picture! And here is her freshly shed skin, called an exuvium.

    Tarantula exuvium


    If you look closely you can see each individual hole where she carefully pulled her legs out of the old skin.


    Now even if you are not keen on spiders, you have to admit, that is pretty cool!

    Celeste Troon, Director of Living Collections

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  • Father of the Year

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    Tags: father's day, button quail, baby animals, birds, public programs

    Created: 6/12/2013      Updated: 8/9/2016

    ‘Father of the Year’ is an annual public program that highlights the best animal dad around the Nature Museum. Every Spring, as new life is booming inside and outside of the museum, we keep our eyes open to observe traits in male animals that contribute to the healthy upbringing of young. Once an exemplary ‘dad’ has emerged, we learn facts about his species and decide if he has what it takes to bestowed this honor. On Sunday, June 16th at 12:00 we will announce the 2013 Father of the Year. Visitors will learn all about the celebrated recipient and what he does to benefit the next generation during the award presentation.

    Male button quail with chick

    Button quail chick

    We started doing this program a few years ago as way of sharing our fondness of the parental instincts of members of our living collection. Visitors are often surprised at how much we might have in common with the rest of the animal world when it comes to ‘bringing up baby’. This program fosters a connection with these notable parents. The 2012 winner of the accolade was the Button Quail- an adorable bird species that resides in the Butterfly Haven. Button Quail males are known to share nesting duties and are be strong protectors of chicks. One day last spring, faint peeping could be heard in the Haven. After a search in between the thick plants, two cute button quail babies were spotted under the wing of one of our males. We knew we had our winner. This year the winner is an equally suitable title holder, but we can’t give it away until the ceremony. Please join us on Father’s Day to learn all about the lauded papa.

    Laura Saletta
    Public Programs Educator

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  • Finally Fieldwork

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    Tags: conservation, fieldwork, blandings turtle, endangered, Biology

    Created: 6/11/2013      Updated: 8/10/2016

    A sure sign of the change of seasons is when we in the Biology Department finally start to get out to do field work. Our Blanding’s Turtle work was severely affected last year by the drought so we had some catching up to do. First order of business, release all last years hatchlings that we had held onto due to a lack of water. We begin by blanking out their individual ID numbers to make them less conspicuous.

    Blanking out Blanding's ID number with marker


    Then we select suitable sites with relatively shallow water, plenty of vegetation for cover and a healthy population of aquatic invertebrates for food. It is always a delightful moment when we watch these little turtles get their first taste of freedom.

    Releasing Blanding's hatchlings into the water


    After all the hatchlings were released we started doing some radio tracking. This can be a slow process as we work to follow the beeps emitted by the transmitter and home in on its location.

    Biologists tracking Blanding's in the water


    This time we had so much water to work in we had a problem reaching the bottom to grab the turtle when we located it. We go from one extreme to the other it seems! Unfortunately our first trail was a bust as we came up with a detached transmitter but we would far rather have this happen than find one that had obviously been removed by a predator.

    A detached radio transmitter


    We can recycle and refit these transmitters so we carefully stowed it and then set of tracking another turtle.

    Biologists tracking turtles through the marsh


    This one led us on a merry dance through all kinds of habitat...

    Biologists wading through the water


    ...before we eventually tracked it down. It is always a great way to end a day of fieldwork by finding a large, strong, healthy turtle.

    An adult Blanding's turtle


    He will have his transmitter replaced and then be rereleased at the exact location he was found. Hopefully he will soon find some female turtles and start work on this year's batch of babies!

    Celeste Troon, Director of Living Collections

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  • The Art of Taxidermy

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    Tags: taxidermy, squirrel, Chicago Academy of Sciences, specimens, chipmunk

    Created: 6/11/2013      Updated: 8/10/2016

    Earlier this month, I had the privilege of learning the art of taxidermy, or, in layman's terms, skinning an animal and stuffing it with cotton and wire. I have to admit that I thought it would be a much more complicated process involving toxic chemicals and specialized safety equipment. In reality, all you need is a sharp knife (preferably a scalpel) and some borax. So long as you're sure to wash your hands afterwards, you don't even need gloves.

    As we waited for our chipmunks to thaw, we spent some time drawing them, taking a few minutes to learn about the contours of their bodies, where their joints are, and how their fur lies. I learned two things during that time. First, I'm not very good at drawing. Second, I learned what a chipmunk really looks like: how its legs move, how the features of its head sit upon its skull, how the color patterns flow across its body. It was all quite intimate.

    Chipmunk on styrofoam

    After bonding with our specimens, it came time to cut into them, from thigh to thigh, right above the genitals, being careful not to cut through the thin layer of muscle separating us from the rodent's stinking bowels. This was a relief, it hadn't dawned on me that by only collecting the skin, we could leave its mess of organs tucked safely in the package nature made for them.

    This was the only time we cut through the skin, the rest of the cutting we performed was done in between the skin and the muscle, delicately cutting away at the layers of connective tissue. We worked our way from that initial incision to the back knees until we could peel the skin up and over them to fit our scissors around the joint without cutting skin. Then, a bit of pressure, a quick snap, and the femur was separated from the tibia and fibula. We'd come back for those later, it was time for the really fun part. Taxidermists have a special tool for getting the tail out, it almost looks like a pair of wire cutters, but instead of cutting them, it’s designed to hold onto the bones in the tail as you slip off the bushy tail. I don't think I could describe the feeling to you. It sounds rather morbid, I'm sure, but it's really quite delightful, almost like popping the cork on a bottle of sparkling grape fruit juice as a kid on Thanksgiving. You gently apply pressure, anticipation mingled with a tinge of fear, then POP, off it goes.

    Things were pretty straightforward from there to the skull, just like pulling off a sock. It was actually pretty meditative, and there were times when I had to stop and take stock of what I was doing, assuring myself that, "Yes, I really am peeling the skin of a chipmunk, and it really is this interesting." This is around the same time that the museum guests started showing up, many of them school groups. There were two facts which many of the children seemed to have difficulty holding in their heads at the same time: these are real chipmunks, and they are dead. One child, nearly at the point of holding these facts together asked, "Are you're fixing it?" Aside from the confusion, there were some wonderfully refreshing moments when a child grasped what was happening and watched with awe rather than disgust. These are the young scientists our country so desperately needs.

    Group of children reacting to taxidermy demonstration

    Steadily working our way up toward the head, casually chatting amongst ourselves, and enthusiastically sharing with the public what we ourselves had learned only a short while ago, it was time for the difficult part. Not only is the face the cutest part of the chipmunk, it's also the most tenaciously wrapped around the skull. The ears, eyelids, and lips can all easily be disfigured by a hand too quick to finish the job. With the help of our resident expert and trainer, we all managed to keep the cuteness intact.

    At last, the skin was off, and it was on to the next stage. The hollow skin was rubbed with borax to dry it out,  and the fluffy side was turned back to face the right side. Next, wires were cut to replace the bones we had removed. One wire reaching from the tip of the nose to the end of the tail, and two reaching from the front to back paw on either side. The central wire was then wrapped in cotton and molded with twine to approximate the shape and size of the body. Because chipmunk tails are rather thin, about a third of the wire was left bare so that what we ended up with looked a bit like a popsicle. This was then gently pushed back through the incision we had made hours ago, all the way up to the adorable little face we had affectionately drawn at the start of our day. The other two wires were then set into place along the sides of the body, pushing it into the superman pose which it will hold for centuries to come.

    Close up of stuffed chipmunk face

    I thought the final step would be sewing it back up, but I'm glad it wasn't (partly because I found it the most difficult). The final step was "to make the specimen look good." I understand that the real reason for this is scientific, for the sake of our collections, but it allowed me to show my respect for the little critter I had just skinned. Gently combing his fur straight and using pins to get his tail and face aligned was a warm way to end what had been a day of cutting, bone breaking, and stuffing. I found it suiting that the process should begin with careful consideration of the creature in its natural form and end with time spent approximating that form. After all, a quick internet search for "bad taxidermy" might make one shudder to think how embarrassed the ancestors of those creatures would be if they were ever to gain sentience.

    Dennis Baker
    Volunteer

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  • Archives: Alfred M. Bailey Bird Photographs from Louisiana

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    Tags: birds, photography, Louisiana, Alfred M. Bailey

    Created: 6/4/2013      Updated: 8/10/2016

    Alfred M. Bailey, director of the Chicago Academy of Sciences from 1927-1936, was an avid nature photographer in both still and motion picture formats.  Bailey was an ornithologist, so the majority of his images are of birds.  The Academy has a large number of Bailey's photographs in their Archives taken on his trips all over the United States and Canada with the intention of recording a variety of species of birds in their natural habitat.  Here are a few examples from his trips to Louisiana:

    Anhinga
    Anhinga with young on nest taken in Louisiana ca. 1930.

    Francis R. Dickinson canoeing
    Francis R. Dickinson canoeing to bird blind for taking images of migrating birds at the Paul Rainey Bird Sanctuary in Louisiana, ca. 1932.

    Laughing Gull on nest
    Laughing Gull with eggs on nest taken in Louisiana ca. 1930.

    Brown Pelican
    Brown Pelican feeding its young taken on shore in Louisiana, ca. 1930.

    Royal Tern Colony
    Close-up of Royal Tern with young in nesting colony taken on shore of Louisiana, ca. 1930.

    Amber King
    Assistant Collections Manager

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  • Academy History - The 1941 Conservation Effort for the Ants at Palos Hills

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    Tags: Archives, conservation, Academy History, Ants

    Created: 6/4/2013      Updated: 8/10/2016

    Conservation has long been a part of the Academy’s history. Today we are actively working with area endangered butterfly species and the Blanding’s turtle, but in our past there were many other conservation efforts for which Academy scientists and staff passionately fought, most often in collaboration with representatives from other agencies or institutions. Some involved preserving large parcels of land like the Indiana Dunes and others focused on one small area or species. 

    One such effort in 1941 saved colonies of the mound building ants, Formica ulkei, that made their home in Palos Hills. The ants came under scrutiny when the land on which they made their home was purchased by the Young Men’s Christian Association (YMCA). The YMCA was concerned that the ants would cause harm to the people that would come visit the campground they were going to establish. Accordingly, they contacted a representative at the Illinois State Natural History Survey to ascertain the best way to destroy the colony. This representative quickly alerted those individuals he knew had been monitoring the colony, and Dr. Eliot C. Williams, Assistant to the Director of the Chicago Academy of Sciences spearheaded the effort. 

    Cover of the Chicago Naturalist

    The Academy published an article on the ants by Alton S. Windsor in its publication, The Chicago Naturalist, entitled “Pyramids of Palos” in October 1939. The colony had been located by Windsor and Dr. T.C. Schneirla in 1931 following local reports of the presence of numerous mounds. They found dozens of mounds at that time and confirmed that the species was Formica ulkei. This particular ant species was only found in a few areas in the Chicago region. The mounds ranged in size from about eighteen inches in diameter and ten to twelve inches in height to as large as seven feet in diameter and three feet above the ground. Windsor continued to visit the site and monitor the ants over the years and he and Schneirla returned together to the site in August of 1939. While some of the mounds had been abandoned due to human intervention or natural progression, the ants as a whole were thriving; a census conducted a few years earlier of just a few acres gave a total number of over 400 mounds!

    Photo from Chicago Naturalist article with caption, "Dr. Schneirla calls at the shrine of one of Chicago's most sensational communities of ants."
    Dr. Schneirla at mound in Palos Hills, from "The Chicago Naturalist" article.

    The YMCA was uninformed as to the scientific importance of the colony when they initially inquired into their removal, but upon receiving letters from Dr. Williams, Jr. and other local scientists, began working with him to formulate a way of using the ant colony to further education about the species and its importance, instead of destroying them. The YMCA and the Academy drew up an agreement in which visitors to the Palos Hills Camp would be informed of the scientific importance of the ants, visitors observing the ants could record their findings, the Academy would have permission to relocate ant mounds located on proposed building sites, and a small sign would be erected at each mound site to help protect the ants “against injury and unthoughtful acts”. In addition, the signs would be numbered so that the observations made by visitors could be accurately recorded and a “history” for each mound could be established.

    Mound marker reading, "Save these ants for science! The Chicago Academy of sciences is making a scientific study of these ants and mounds. Please do not touch or otherwise harm any mound -- this is an ant sanctuary!"

    Scan of a mound marker sign from the Academy's Insitutional Archive used to mark and number each ant mound.

    Today this species is no longer present in Palos Hills and not much is known about the effort and why and when it ended or even where the proposed visitor records are now. Williams was drafted in July 1942 and served in the Army until March 1946. Many others from the Academy and the scientific community joined Williams, leaving the Academy and other organizations with a skeletal staff during the war years.  It was perhaps this absence and the increased responsibility of those who remained stateside that led to the decline in the oversight of this site, but we can only speculate. While this effort did not culminate in the continuation of the Formica ulkei at Palos Hills in perpetuity, the open dialogue created on both sides of the issue resulted in fruitful discussion and compromise.

    For further information:

    Greenberg, Joel, ed.  Of Prairie, Woods, and Water: Two Centuries of Chicago Nature Writing. Chicago:  University of Chicago Press, 2010, pp. 457-468.

    Windsor, A.S. “Pyramids of Palos.” The Chicago Naturalist, Vol. 2, No. 3: October 1939, pp. 67-72, 91.

    Chicago Academy of Sciences Institutional Archives

    Amber King
    Assistant Collections Manager

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