PHYTATM CHORD AT A 



13 



Affinities. — Tlie inclusidn of l.lic HcmichoiMla in the phylum 

 Chonlata is an anungeniont the propriety of wliich is not uni- 

 versally admitted, and is carried out here partly to obviate the 

 inconvenience of erecting the class into a separate j)hyluni. On 

 the whole, however, there seems to be sufHcient evidence for the 

 view that, if not the existing representatives (jf ancestral Chor- 

 dates, they are at least a greatly modified branch, taking its origin 



ret 



St 



Flfj. 714.— Khabdopleura. A, Entire zooid. a, mouth; />, anus; <■, stalk of zooid ; il , pro- 

 boscis ; e, intestine ; /, anterior region of trunk ; ii, one of tlie tentacles. (After Ray Lankestcr.) 

 B, Diagram i.f the organisation ; median longitudinal section, seen from the left, a arm ; 

 ail, anal prominence ; i-ol. collar ; col. ne. eoUar-nervo ; ';. s. cardiac sac ; int. intestine ; 

 )/t. mouth; I'tc. " notochord " ; «. o3sopliagus ; pr. proboscis; pr. c. proboscis-ctelome ; rrt. 

 rectum ; at. stomach ; tc. tentacles ; tr. c. trunk-C(i;lome ; v. ,<. ventral nerve. (After 

 Sohepotieff.) 



from the base of the chordate tree. The presence of the pre- 

 sumed rudimentary representative of a notochord and of the gill- 

 slits seems to point in this direction. It should, however, be stated 

 that by some of those zoologists by whom the members of this 

 group have been most closely studied, their chordate affinities are 

 altogether denied. If the Hemichorda are primitive Chordates, 

 the fact is of special interest that they show remarkable 



