Courtesy Bo Wang and Phillip Newmark, HHMI/University of Illinois at Urbana-Champaign

Two hundred fifty million people worldwide require treatment for schistosomiasis, also known as bilharzia, a disease that ravages internal organs. Schistosomiasis is caused by parasitic flatworms that cycle between two hosts: freshwater snails and humans. Seeking ways to stop the transmission, biologists at the University of Illinois are studying the worm’s reproduction. This summer, they dyed and sectioned snail muscle tissue. Inside, they saw flatworm stem cells, which develop into thousands of larvae about 300 micrometers long. This image is color-coded to show relative depth; closer objects glow orange and more distant objects, green. Now, the scientists are studying how the stem cells develop, which could lead to ways to halt the parasite’s growth.

_This article originally appeared in the December 2013 issue of _Popular Science.