THE STRUCTURE OF THE LARVA OF LANICE CONCHILEGA IO5 



The otocysts were first observecl in this larva by Claparede, who con- 

 sidered them to be a quite uncommon feature, the only other Polychœta 

 then known to possess thèse organs being Areiiicola. Since then however 

 they hâve been discovered in several other species, and a full account of 

 them was given recently by Fauvel (1907). 



Internai structure. The ahmentary canal consists of an œsophagus, a 

 stomach and an intestine. The mouth leads directly into the œsophagus, 

 which is long and narrow and ciliated. A large number of mucous cells are 

 distributed between the epithelial cells of the lining of the œsophagus. 



The stomach is voluminous, and forms the greater part of the alimen- 

 tary canal. It is bent over on itself, so that the alimentary canal is twisted 

 into a loop, a condition which disappears in the adult state. 



The cells forming the epithelial lining of the stomach are to a large 

 extent vacuolated, and in many instances were founcl to be infested with a 

 species ofmicroorganism. 



The food of the larva, we may mention incidentally, consists mainly 

 of Diatoms, among which we noticed principally Chœtoceros and Bid- 

 dulphia. 



The stomach leads into the terminal section of the alimentary canal, 

 which forms the intestine and which, like the œsophagus, islinedthroughout 

 with ciliated epithelium. 



The segmentation of the coelom is incomplète, one septum only exists 

 in the anterior région of the body cavity, the middle région containing the 

 gastric part of the alimentary canal is undivided. 



A séries of septa, corresponding with the external segmentation, are 

 however présent in the posterior région of the coelom which is traversed" 

 by the intestine. 



As in the adult Lanice, a mass of glandular tissue arises from the 

 ventral wall of the coelom, in the anterior part of the body. This tissue 

 surrounds the ventral nerve cord and seems by its upward growth to push 

 the œsophagus upwards with it. 



The nervous System consists of a cérébral mass of nerve tissue situated 

 in the head, above the œsophagus. An œsophagial commissure connects this 

 mass with the ventral nerve cord, which extends some distance towards the 

 posterior end of the body, without completely reaching the extremity. 



Blond l'essels. We hâve not found any traces of blood vessels in the 

 larva at this stage. 



