204 AQUATIC MICROSCOPY FOR BEGINNERS. 



verse fission. The podal spines are in two rows, the 

 clflsters containing four to eight spines each, being . 

 usually most numerous toward the posterior extremity. 



The mouth is large, oblique, and surrounded, by 

 many very short stiff hairs. It is often used, when 

 the worm is on the slide, as a sucker, clinging to the 

 glass and drawing the body towards it. The intes- 

 tine, in the species common in the writer's vicinity, is 

 much and irregularly constricted, a feature which 

 gives it the appearance of a series of various-sized 

 pouches. 



The blood is pale or colorless. The blood-vessels 

 are distinct as narrow, pulsating, longitudinal tubes. 



Chatogdster is one of the most interesting forms on 

 account of its perfect transparency and the absence of 

 bristles, which allows an uninterrupted view of the 

 whole surface, as well as of the internal organs. 



4. LUMBRfcULUS. 



The body is translucent, but often brightly colored 

 at the sides or in the central parts. 



The blood is bright red, and the dorsal vessel gives 

 off several short, lateral, pulsating branches in each 

 segment of the body. These short branches fre- 

 quently approach the surface, and give it a mottled ap- 

 pearance, the spots fading and reappearing as the 

 branches contract and expand. 



There are four rows of podal spines, with but two in 

 each cluster, each being curved, forked at the end,* 

 and with an. enlargement or shoulder near the center 



*Since this was written a species has been observed with undivided 

 podal spines. It has been included in the Key. 



