u 



It is thus evident that in the plane of the tentacles there is a 

 mesentery or septum stretching across the body obHquely and 

 separating the blastocoele from the trunk body cavity. The 

 blastocoele is traversed by contractile bands, and is more or less 

 completely hned by cells. The latter are especially well developed 

 in the region of the stomach and oeso^^hagus and the stomodeal 

 wall, and give rise to blood cells by division. The blood cells 

 soon become yellow and then red with haemoglobin. The trunk 

 body cavity consists of a parietal layer surrounding the body, a 

 mesentery connecting the ventral wall of the body with the stomach 

 and intestine, a splanchnopleure surrounding the stomach and 

 intestine, and the se]3tum. The lophophoral body cavity Unes 

 the adult tentacles and the part of the adjoinmg wall of the 

 body between the tentacles and the septum ; its visceral la^-er 

 separates the cavity from the blastocoele. In the tentacle a 

 mesentery is formed on the outer wall, which expands in the centre 

 into a blood vessel opening into the blastocoele. A proliferation 

 of the splanchnopleure of the trunk body cavity just below the 

 septum and extending downwards for a short distance on the 

 dorsal aspect of the stomach gives rise to a blood vessel which is 

 at first a closed structure but later becomes open in the larva 

 and Hkewise coinmunicates with the blastocoele. A lateral vesseJ 

 is also developed on the lower left aspect of the stomach, and this 

 vessel is produced into numerous bUnd diverticula. These vessels 

 are mdicated in the figure of J. brancJiiata (Fig. 1). 



The nephridia are of ectodermal origin. They occur as 

 ingrowths in the neighbourhood of the anus, and like the latter 

 therefore are post-blastoporal in origin. By the growth of the 

 larva in this post-blastoporal part of the body the anus and the 

 nephridia come to be widely separated, the anus remaining at 

 the posterior end of the body and the nephridia coming to occupy 

 a position just posterior to the tentacles. They project into the 

 blastocoele in front of the septum, and the bifurcated bhnd end 

 is clad with solenocytes as has been described by Goodrich and 

 others. The influence of the action of these is shown by the 

 position taken up by the blood cells. These are arranged in two 

 heaps near the bhnd end of each nephridium, and it is evident 

 that the heaps are of physiological origin for they tend to be broken 

 up when the larvae are killed. 



