ON DEVELOPMENT ETC. OF PIIOKONIS. •)// 



V.V.). At the place whore the degenerating stomach divevticulum 

 still persists, the sinnses completely hlend together into one lai-ge 

 l)lo(»d vessel corresponding to the ventral vessel of ^MastePvMAN 

 (fig. 64 c, V.V.). This vessel acqnires a definite form at a more 

 anterior region of tlic (eso])hagns, becoming lined on its sides with 

 a tliin mesohlastic wall (fig. 64 r/, v.r.). At ahout this level the 

 dorsal vessel {<J.v.) on the œsophagns l^ecomes a small canal, snch 

 as we know it to he in the adult animal. According to my 

 observations, the large ventral vessel opens at this stage not by 

 two Imnichcs, as is the case in the adnlt, but by one directly into 

 the ring vessel. To my great regret, however, I have not been 

 able to stndy microscopically the larvie in which the communica- 

 tion between the ring vessel and the dorsal oi- ventral vessel was 

 in the process of being established. 



Xow we see that the dorsal vessel of Actinoiroclia corresponds 

 to the afferent, and the ventral vessel to the efferent vessel of the 

 adult. The sinuses around the stomach, which have newly 

 arisen during metamorphosis, develop into the complicated organ 

 of the adult. 



Nephridia. At the stage when the metamorphosis takes 

 place, the nephridia do not show any important alteration inform 

 and structure from those of the swinnning larva ; the excretory 

 cells (e.rc.c) are found still attached to the blind end of the 

 nephridial canal (fig. 64 /", ncp.c.) and the external nephridial pores 

 open behind the septum (fig. 64 e, nep. o.). In fig. 64 e we 

 notice only that the nephridia as a whole have shifted to a more 

 dorsal position than that occupied in the preceding stages (compare 

 with fig. ~)0c). This shifting of position becomes more and 

 more marked as the metamorphosis advances, so that when the 

 process is nearly finished, the nephridia on both sides come close 



