398 Illinois State Laboratory of Natural History. 



The brain is slightly longer than wide, and is deeply 

 cleft both anteriorly and posteriorly as in P. looigiseta 

 ('84, Vejdovsky, Taf. II., Fig. 13). 



The alimentary tract agrees with that of P. longiseta 

 and of Leidy's species. The glandular ventricle is in the 

 anterior part of VIII, and is followed by a narrow part 

 of the intestine which is convoluted in IX and opens 

 into the wider region of the intestine in the posterior 

 part of that somite. In older specimens these regions 

 are very distinct, but in those recently formed by bud- 

 ding the differentiation is much less obvious. As in P. 

 longiseta^ septal glands are present in III-V, of which 

 those in IV and V are large. 



A pair of contractile vascular trunks connects the dor- 

 sal and ventral vessels in each of somites III-VII, being 

 situated just in front of the posterior septum in each. 

 While they are all conspicuous, yet those of VI and VII 

 are a little larger than the others, though not so tnuch 

 dilated as those of P. longiseta as figured and described 

 by Vejdovsky. A pair of non-contractile vessels branch 

 off from the dorsal vessel just posterior to the brain. 



The first pair of nephridia is in IX. An examination 

 of more than thirty specimens with reference to their 

 location has shown no variation in the position of the 

 first pair, but in five instances the ninth somite contained 

 but one nephridium. The next following somites usu- 

 ally contain but a single nephridium, although in eight 

 per cent, of the cases two nephridia were present, and in 

 nine per cent, the nephridia were entirely wanting. In 

 at least ninety per cent, of the instances observed, when 

 but one nephridium was present it belonged to the left 

 side of the somite. In P. longiseta the first nephridia 

 are stated to occur in somite X, and, to my knowledge, 

 there is no record of such variability in the number of 

 nephridia in each somite as characterizes P. leidyi. The 

 nephridiopores are a little anterior to the ventral setsB 

 and sliffhtlv mesad of the same. 



