238 AN INTRODUCTION TO ZOOLOGY. 



venience. It received the group name of Enteeo- 

 PNEUSTA before that of Hemichordata was bestowed 

 upon it on account of its possessing a notochord. 

 The larva resembles that of an Bchinoderm. The 

 animal receives its generic name, acorn-tongued, from 

 the shape of its contractile proboscis, which serves as 



Fig 86. — Balatioglossus, a link between vertebrates and invertebrates, sbow 

 iiig proboscis and lateral gill-slits. 



a locomotive organ. The notochord arises in connec- 

 tion with the pharynx (throat). There is a dorsal 

 nervous cord. In respiration, the water goes in at 

 the mouth and out at the gill-slits, which in structure 

 resemble those of Ascidians, consisting of numerous 

 small holes. In the young animal, however, there is 

 only a single pair of gill-slits. 



