B ALA NO GL OSS US. 



243 



consisting externally of a collar-like expansion of the 

 integument, with free anterior and posterior margins over- 

 lapping the base of the proboscis in front and the anterior 

 portion of the gill-slits behind. 



In the ventral middle line, at the base of the proboscis 

 and concealed by the collar, is situated the mouth (Fig. 

 113). Following behind the collar is the region of the 

 trunk or body proper, which, in the adult of some species, 

 reaches a relatively enormous length, even extending to 



Fig. 113. Larva of Balanoglossus Kowalevskii, with five pairs of gill-slits; 

 from the right side. (After BATESON.) 



a. Anus. a. p. Temporary pedicle of attachment, c. Collar, ch. Notochord. 

 g.s. Gill-slits, m. Mouth, pr. Proboscis. 



two or three feet. The ectodermal covering of the body 

 consists in general of ciliated cells, among which are scat- 

 tered unicellular mucous glands ; the cilia, however, appear 

 to be more prominent on the proboscis than elsewhere. 



In the region of the trunk, which immediately follows 

 upon the collar region, there are a great number of paired 



