280 CLASSIFICATION OF CHOEDATA. 



rod between the nervous system and the gut. Couch describes 

 this fascinating little creature amongst the British Fish. 



Another form to be mentioned here is the -worm-like Baluno- 

 glossus, which Mr Bateson has shown to have a dorsal axial 

 rod (notoohord) and a dorsal hollow nervous system, besides a 

 series of gill-slits, like a fish. 



The whole of those animals that possess a dorsal nervous 

 system and a notoohord during some period of their existence 

 are best known, then, as Chordata. 



The Chordata can again be divided into two sections — namely, 

 the Aeraiiia and the Oraniota. The former contains those lowly 

 intermediate forms which Mr Bateson classifies as foUows : — 



1. Hemichordata (Balanoglo&sus). 



2. Uroohordata (Ascidians). 



3. Cephalochordata (Aniphioxus). 



"Whilst Fish, Amphibia, Reptilia, Aves, and Mammalia may be 

 placed in a fourth division — 



4. Vertebrata. 



Thus for the old term Vertebrata we now substitute Chordata, 

 and use the term Vertebrata only for those Chordata with a 

 craniiim and a distinct skeleton, either cartilaginous or osseous, 

 so that the Chordata tabulate ns follows ; — 



1 1. Hemichordata. 

 Acrania (no brain) j 2. Urochordata. 



3. Cephalochordata. 



Pisces. 

 Amphibia. 

 Oraniota {brain present) 4. Vei-tel)rata "! Reptilia. 



1 Aves. 

 I Mammalia, 



Chordata 



