CHORDATA 



.''.i 



Balanoglossus (Fig. 272) is a murine animal, living in the sand 

 along the shore, and has a soil, wormlike body, ordinarily from 

 ten to fifteen centimeters long. It is nearly cylindrical and 

 exhibits three regions, an anterior proboscis, a short collar, and 



the elongated trunk. At the point where the proboscis joins 

 the collar is the mouth on the ventral side, and on the dorsal 

 side, a pore connecting with a part of the body-cavity. Just 

 posterior to the collar is a series of slits on each side of the 



FIG. 270. Cephalodiscus, gelatinous investment. (After Mcintosh, from Parker and 



Haswell's Text-book.) 



trunk on the dorsal surface ; these are the gill slits and connect 

 with the anterior portion of the alimentary canal. The gill 

 slits increase in number during the life of the individual, new 

 openings forming at the posterior end of the series. In some 

 species there is a ridge on each side of the anterior portion oi 

 the trunk, the genital ridge, caused by the gonads or germ- 

 glands situated within. The rings which appear on the pos- 

 terior portion of the trunk are purely superficial. The glands 

 of the skin secrete a viscid substance which serves to cement 



