34 CHAPTERS ON THE NATURAL HISTORY 



myriopods, insects, spiders, and the various allies of these, living 

 and extinct. 



Passing to the Vertebrata, we meet at the very threshold of 

 this phylum, as stated above, forms in regard to the taxonomy 

 of which biologists by no means hold a unanimous opinion. I 

 am inclined to think, however, that waiving such little violence 

 as may be done, in any particular instance, the gain for conven- 

 ience and classificatory simplicity will so far outweigh it that, in 

 the light of future research, not only will Ampliioxus, the Tuni- 

 cata, and Balanoglossus be admitted, with Cuvier's Vertebrata, in 

 the phylum Vertebrata, but both Cephalodiscus, as well as Bhab- 

 dopleura, will be placed there, associating them with Balanoglos- 

 sus. Granting the admission of these three groups as the Ceph- 

 alochorda (Amphioxus), the Vrochorda (Tunicata), and the Hemi- 

 ohorda (Balanoglossus), Vertebrata, as the Craniata, will stand 

 as a fourth one, the whole constituting the great phylum of the 

 Vertebrata. 



The Craniata may be primarily divided into two main divi- 

 sions, the first, the Gyelostomata, including the hagfishes (Myx- 

 iuc) and the lampreys (Petromyson). They are limbless, scale- 

 less, round-mouthed, almost jawless forms that lead up to the 

 fishes. 



The second division of the Craniata — the Gnathostornata — in- 

 cludes the main vertebrate groups of Fishes, Amphibians, Rep- 

 tiles, Birds, and Mammals. In a brief chapter, such as the one 1 

 am now writing, it becomes out of the question to discuss the 

 minor divisions of these great groups, much less the morphologi- 

 cal considerations upon which they are based. I must not neg- 

 lect to point out, however, that Birds are linked to Reptiles 

 (Sauropsida), as are Fishes linked to Amphibians (Ichtlu/opsida). 

 many extinct forms corroborating the two alliances. 



