464 The Protochordata 



Bateson in the more primitive genus Dolichoglossus, studied 

 by him. This adult animal may be, indeed, a worm as it appears, 

 but the presence of gill-slits, the existence of a rudimentary 

 notochord, and the character of the central nervous system 

 are distinctly fish-like and therefore vertebrate characters. 

 With the Chordates, and not with the worms, this class, Enter op- 



FIG. 276. Glossobalanus minutus, one of the higher Enteropneustans. 

 (After Minot.) 



neusta (evrepov, intestine; nveiv, to breathe), must be placed 

 if its characters have been rightly interpreted. It is possibly 

 a descendant of the primitive creatures which marked the 

 transition from the archaic worms, or possibly archaic Echino- 

 derms, to the archaic Chordate type. 



It is perhaps not absolutely certain that the notochord of 

 Balanoglossus and its allies is a true homologue of the 

 notochord of the lancelet. There may be doubt even of the 

 homologies of the gill-slits themselves. But the balance of 

 evidence seems to throw Balanoglossus on the fish side of the 

 dividing line which separates the lower Chordates from the 

 worms. 



It may be noticed that Hubrecht regards the proboscis 

 of various marine Nemertine worms as a real homologue of the 

 notochord, and other writers have traced with more or less 

 success other apparent or possible homologies between the 

 Chordate and the Annelid series. 



Classification of Enteropneusta. Until recently the Enterop- 

 neusta have been usually placed in a single family or even in a 

 single genus. The recent researches of Professor J. W. Spengel 

 of Giessen and of Professor William Emerson Ritter of the Uni- 

 versity of California, have shown clearly that the group is much 

 larger than had been generally supposed, with numerous species 



