SOME AQUATIC WORMS, ETC. 191 



irregularly constricted, a feature which gives it the ap- 

 pearance of a series of various - sized pouches. The 

 blood is very pale or colorless. The blood-vessels are 

 distinct as narrow, pulsating, longitudinal tubes. ChcB- 

 togdster 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 sur- 

 face, as well as of the internal organs. 



4. LUMBKICULUS. 



The body is translucent, but often brightly colored at 

 the sides or in the middle 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 frequently approach the surface, and give 

 it a mottled appearance, the spots fading and reappear- 

 ing as the branches contract and expand. There are 

 four rows of podal spines, with but two in each cluster. 

 They are curved, forked at the end,* and have an en- 

 largement or shoulder near their centre. At a short 

 distance from the attached end of each pair there is 

 often to be found another pair, which are small and 

 may be overlooked on the front of the body when the 

 worm is not dividing transversely. When it is under- 

 going transverse fission the posterior part may be so 

 well supplied with these small secondary podal spines 

 that their number and arrangement may confuse the 



* Since this was written a species has been observed with undi- 

 vided podal spines. It has been included in the Key. 



