ON THE DIPLOGHORDA. 309 



consist of a single layer of colnniiiar ciliated cells enclosing a 

 fine lumen. 



Wagener (20) figures one of these organs, and describes its 

 appearance in the live larva. He says that "from its free 

 broad sides there project many small stumpy pointed knobs ou 

 long stalks, which spread about in all directions like a bouquet 

 of flowers^' (translation). This description plainly indicates 

 that the mass of cells seen in prepared sections around the 

 tubes is formed by a number of cells attached by long pro- 

 cesses to the mouth of the funnels. In fact, a few preserved 

 specimens give indications of this arrangement. We thus 

 arrive at a pair of collar nephridia resembling almost identi- 

 cally the structure of the ne[)hridia as described by Boveri (la) 

 in Amphioxus. A point which cannot be fully entered 

 into here is the fate of these collar nephridia, so evidently homo- 

 logous with the collar pores of Cephalodiscus audBalano- 

 glossus. If they become the nephridia of the adult the open- 

 ings into the collar region must be lost, and fresh openings 

 must be acquired into the trunk ccelom. Caldwell (2) says, 

 "The large canals remain as the paired nephridia of 

 the adult." We may, however, recollect that the adult 

 nephridia open on the dorsal side and the collar nephridia on 

 the ventral side. Further than this, there are described below 

 other organs, which may possibly be the rudiments of the true 

 nephridia. 



Trunk Coelom. — The ccelom of the trunk has the same 

 characters as that of the collar. It is continued dorsally 

 forwards for some way almost to the level of the notochords. 

 There is apparently no dorsal mesentery, but a ventral me- 

 sentery is continued throughout the length of the trunk, and 

 suspends the iutestiue. At the perianal area are a pair of 

 organs which I have not fully made out, but they may be the 

 rudiments of the trunk nephridia. They lie in the haemocoele 

 space immediately below the ciliated band, and are thin- 

 walled. They have an internal opening into the trunk coelom, 

 and apparently open to the exterior on either side of the anus. 

 Their walls are of the same nature as those of the coelom, 



