CHAPTER V 



THE WORM-LIKE PROTOCHORDATES CLASS Enteropneusta 



THE last, and at the same time the lowest, group of the Proto- 

 Balanoglossus c jj Or ^ ates j s typically represented by the marine Balanoglossus. Liv- 

 ing buried in the sand or mud of the seashore, these worm-like "creatures exhale 

 a peculiar odor resembling that of the 

 chemical substance termed iodoform, and 

 secrete a copious supply of slime, to which 

 adhere particles of sand, thus forming 

 a protective tube for their bodies. At the 

 front extremity of the creature, writes 

 Mr. Willey, " there is a long and extremely 

 sensitive proboscis, which is capable of 

 great contraction and extension, and is in 

 the living animal of a brilliant yellow 

 or orange color. Behind the proboscis 

 follows a well-marked collar region, con- 

 sisting externally of a collar-like expan- 

 sion of the integument, with free anterior 

 and posterior margins overlapping the 

 base of the proboscis in front and the ante- 

 rior portion of the gill slits behind. (The 

 gill slits are seen in our illustration below 

 the collar. ) In the ventral middle line, 

 at the base of the proboscis, and concealed 



by the collar, is situated the mouth. 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 two or three feet. The ectodermal covering of 

 the body consists in general of ciliated cells, among which are scattered 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 openings on the dorsal side of the 

 body placing the anterior portion of the digestive tract in communication with 

 the outer world. These are the gill slits, and they are arranged strictly in consecu- 

 tive pairs to the number of upward of fifty in the adult. In their structure, and 

 more especially in the possession of tongue bars, they bear a remarkable resem- 

 blance to the gill slits of the lancelet. This is particularly striking in young individ- 

 uals. As the adult form is approached in the development, the bulk of the gill slits 



(2951) 



A YOUNG BAI.ANOGLOSSUS. 



(Much enlarged.) 



