256 AQUATIC MICROSCOPY FOR BEGINNERS. 



c. Extremities acute, sometimes prolonged, Lophopus, 



Fig. 175.* 



d. Spines in a single, marginal series, double-hooked, 



Fectinatella, Fig. 176. 



d. Spines in two rows, variously hooked, Cristatella, 

 Fig. 177. 



Those who desire to be fully informed as to the 

 anatomy of the charming creatures which form the 

 group of the fresh-water Polyzoa, and to distinguish 

 the several species, are referred to Professor Alpheus 

 Hyatt's work on "The Polyzoa," published by the Es- 

 sex Institute, Salem, Mass., and to Professor Joseph 

 Leidy's papers on the subject in the Journal of the 

 Academy of NaturUl Sciences of Philadelphia. 



*The statoblasts of Lophopus are here keyed and figured, as the 

 reader may at some time find them before he is so fortunate as to dis- 

 cover the Polyzoan itself, and thus be led to search for the animals, 

 the winter eggs having put him on their track. 



