'376 i. ÏKEDA 1 



into the iiifrarieptal cavity (fig. 64 f, dir.). The vacuok^s in the 

 cell of the diverticular wall disappear at this period, and 

 the di\erticulum itself is innnediately afterwards wholly ohliterated, 

 piohahly as the result of a histological ati-ophy. The stomach wall 

 does not essentially differ in structure from that of the larva. 



Mesoblastic Orgaiu. Among the mesoblastic organs the vas- 

 cular system undei'goes most noteworthy clianges. IMastehman 

 has maintained that this forms a completely closed canal system 

 even in the free swimndng stage of tlie larva. So far as I have 

 heeii able to ascertain, tlie closing \\\) dI" the vessels into a conti- 

 nuous system occurs after the critical moment of metamorphosis, 

 JLiving ah'cady described my own observations res])ecting the origin 

 of tbc ling vessel of the adult, T will now describe other vessels 

 which arise during metamorphosis. 



Fig. 64« shows a cross secti(jn of the I'ooi near the posterior 

 extremity where the alimentary canal is Ijent upon itself. Here 

 we see the cut ends of three contractile capillaries (v.c.) and three 

 sinuses (.s.-s.) in the stomach walls. A comparatively wide space 

 {d.v.) is found intercepted l^etween the two liml)S of the alimentary 

 canal. This space corresponds to the most posterior portion of the 

 dorsal vessel, which, if traced further posteriori v, shows itself to 

 be continuous with l)oth the capillaries [v.c.) and the sinuses (s.-y.). 

 A short distance more anteriorly, the dorsal vessel divides into 

 two parts each of which attaches itself to a lindj of the alimentary 

 canal ; still more anteriorly the branch on the intestine disap])ears. 

 In that ])orti(jn of the stomach which lies close to the (esophageal 

 tract, the dorsal vessel becomes envelo])ed with a thick muscular 

 sheath which we have before seen in Acfuioirocha (fig. 64/', d.v.). 

 The vascular sinuses gradually tend to unite into one common sj)ace 

 lying on the ventro-lateral side of the gut (lig. 64 h, u.a.; iig. 64 c, 



