364 TEXTBOOK OF ZOOLOGY 



ventral cord rimning longitudinally on the floor of the trunk. The 

 ventral cord certainly is not a chordate characteristic, but the domi- 

 nance and hollow structure of the anterior portion of the dorsal 

 one, represent features which are homologous to the central nervous 

 system of higher chordates. 



Excretion seems to be accomplished by a mass of vascular tissue 

 (glomerulus?) located in the proboscis just anterior to the heart. 

 The excreted materials are received by the water in the proboscis 

 cavity (coelom) and pass out the pore with the water as it is ex- 

 pelled. These animals are dioecious, with gonads in the form of a 

 genital ridge extending leng-thwise along each side of the anterior 

 portion of the trunk. The mature germ cells escape through the body 

 wall, are fertilized in the water, hatch out and become tornaria 



Apical plate 



Mouth 



Proboscis 

 ccelum 



Anus 



Fig. 211. — Tornaria larva of Hemichorda. (From Hegner, College Zoology, pub- 

 lished by The Macmillan Company, after Metchnikoff . ) 



larvae, which are globular in shape and form a pattern of ciliated 

 bands over the body. In this respect and in habit of life these 

 larvae resemble the larvae of the echinoderms. On this basis a 

 theoretical relationship has been proposed. Until relatively recent 

 times this larva was mistaken for a form of adult nonchordate ani- 

 mal and went under the genus name of Tornaria. 



Dolichoglossus and its subphylum, though lacking in complete 

 conformity to chordate characteristics, is classified here because of 

 the diverticulum supposedly representing a rudimentary notochord, 

 the gill clefts in the alimentary canal, and the dominance and 

 grooved structure of the dorsal nerve cord. The group includes 

 Cephalodiscus and Rhaldopleura which are colonial forms living in 

 deep sea. 



