Anatomy and Histology of a Neiv Eartlnvorm. 53 



The third division of the intestine extends from somite 20 

 nearly to the posterior end of the body. It is similar to the 

 preceding more inflated part, being thin-walled and sacculated, 

 and is pretty uniform in diameter throughout. 



Towards the vent the canal again changes in character to 

 form the rectum. Exteriorly there is little to distinguish this 

 division from the intestine which precedes it, but cross sec- 

 tions show a decided thickening of the wall, due to an increase 

 of muscle tissue and to the great development of the lining 

 epithelium. 



No intestinal coeca have been observed. 



The typhlosole might easily escape observation on casual 

 study. It is represented by a low ridge projecting into the 

 cavity of the intestine from the dorsal side and extending from 

 somite 23 backwards. It begins to decrease in size behind 

 somite 40, and soon becomes scarcely perceptible. 



The Vascular System. 



The vascular system of this genus differs from that of 

 Lumbricus in being simpler, — the subneural vessel and the com- 

 missural vessels putting the latter in communication with the 

 dorsal vessel being here wanting. With certain of the post- 

 clitellian group of genera, Diplocardia shows marks of closer 

 relation with respect to these vessels. 



The dorsal vessel is distributed upon the pharynx in the 

 usual manner. From the pharynx it extends backwards over 

 the gizzard as a simple tube without branches until just before 

 the dissepiment between somites 6 and 7, where very small lat- 

 eral branches pass around the posterior part of the gizzard and 

 enter the subintestinal vessel below. Immediately behind the 

 dissepiment between somites 6 and 7, the dorsal vessel divides 

 into two trunks, which again unite to pass through the dissepi- 

 ment between somites 7 and 8. In somites 8 and 9 the same 

 thing occurs, accompanied by an increase in the size of the 

 dorsal vessel and its lateral branches. In somites 10, 11, and 

 12 the lateral branches become greatly enlarged, equaling in 

 diameter the dorsal vessel in these somites. All these "aortte" 

 are loosely bound to the posterior septa of the somites in which 



