On the Classification of Animals. 



261 



namely, Mammals, Birds, Reptiles, and Fishes, — three of which 

 are typical, of different grades, parallel with the above. 



(2.) The classes of Articulates are but three, Insecteans, Crus- 

 taceans, and Worms. I have already shown that the three di- 

 visions of Insecteans, namely Insects, Spiders, and Myriapods, 

 are distinguished by characteristics analogous to those which 

 separate the divisions of Crustaceans, — Decapods, Tetradecapods, 

 and Entomostracans. The facts on this point are briefly pre- 

 sented on page 97- Insects and Spiders do not, in fact, differ 

 more widely in external form or in structure than Decapods and 

 Tetradecapods. 



Insecteans and Birds express in different ways the same 

 type-idea, — that of aerial life, Birds being flying Vertebrates, and 

 Insects flying Articulates ; and, in accordance, they are of the 

 same grade of type, both being hetatypic. This follows, further, 

 from the fact that there are but two grand divisions of Insec- 

 teans above the degradational division, that of Worms. 



(3.) Among Mollusks, there are two well-characterised classes, 

 the first including the ordinary Mollusks ; the second, the Asci- 

 dioids, or the Brachiopods and Ascidians, which are mostly at- 

 tached species and thus hemiphytoid. Besides these, there are 

 the Bryozoans, which either make a third division under the As- 

 cidioids (Edwards having long since pointed out their relations to 

 the Ascidians) ; or they constitute a third class of Mollusks, 

 characterised by being polyp-like both in external appearance 

 and in being attached, and hence doubly hemiphytoid. 



(4.) The Radiates are all degradational in their relations to 

 the animal-type. But under the Radiate-type^ the species of the 

 first two classes are within type-limits, while those of the third 

 are degradational, since almost all are attached and very inferior 

 in type of structure, being the most phytoid of phytoid animals. 

 The grades of structure, as marked in the digestive system, are as 

 follows : (1.) Having approximately normal viscera, as in Echino- 

 derms ; (2.) Having, for the digestive system, only a stomach 

 cavity, with vessels, imbedded in the tissues, radiating from it, as 

 in Acalephs ; (3.) Having, for the same, no system of viscera or 

 radiating vessels ; but only a central stomach surrounded by a 

 cavity more or less divided at its sides by partitions as in Polyps. 



The following table presents the relations and the parallelisms 

 of these classes, and of each to the subkingdoms : — 





Subkingdoms. 



Vertebrates. 



Articulates. 



Mollusks. 



a. 



Vertebrates. 



Mammals. 







iS. 



Articulates. 



Birds. 



Insecteans. 



Ordinary. 



7- 



Mollusks. 



Reptiles. 



Crustaceans. 



Ascidioids. 



D. 



Radiates. 



Fishes. 



Worms. 



Bryozoans? 



Echinoderms. 

 Acalephs, 

 Polyps. 



NEW SERIES. VOL. XIX. NO. II. APRIL 1864. 2 L 



