18/3.] 



the Invertebrata in relation to Evolution. 



223 



Scheme of Classification of Invertebrata. 



Leading Types of Protozoa, aggregate or compound. 



Collospkajra. 



Thalassicolla. 

 Gregarina. 



Cestoidea. 



Trematoda. 



JS~ematoidea> 



2. 



Porifera. 



Polycystina. 



Corresponding simple forms. 



Actinophrys. 

 Gromia. 



Acantkoinetra. 

 Podocyrtis. 



Derivative types. 



Infusoria. Noctilucida?. 



Turbellaria. Rotifera. 



Sipunculidse. Annelida. 



Echinodei'mata. Articulata. 



4. 



Foraminifera. 



Amoeba. 

 Difflugia. 



Ccelenterata. 

 Molluscoida. 

 Mollusca. 



So as not to complicate the Table, I thought it better to supplement 

 it with the definition of the four leading types of compound Protozoa. 



1. In the Collosphsera type, the sarcode-bodies lie at some distance 

 apart and are always distinct. 



2. In the Porifera type the sarcode-bodies are closely approximated or 

 • confluent. 



3. In the Polycystina type the sarcode-bodies are concentric and con- 

 nected by radiating stolons. 



4. In the Foraminifera type the sarcode-bodies are connected by 

 stolons in linear series or some order of juxtaposition. 



If it is incumbent upon the developmental hypothesis to derive the 

 Vertebrata from the preexisting Invertebrata, the only line through 

 which it would be possible to trace their descent is that leading from the 

 Protozoa to the Mollusca proper, or the fourth series of the Table. It 

 would also appear that the Entozoa, Echinodermata, and Articulata 

 appertain severally to separate series of their own ; and whatever may 

 happen by-and-by, it would be difficult to find, in the present fauna of 

 the globe, a single form clearly deducible from any of them. 



The habit of life of the Entozoon, the peculiarity of structure of the 

 Echinoderm, and the very perfection of organization of the Articulata, as 

 it were, preclude their evolution into any other existing type. To use a 

 common phrase, they may be said to lead nowhere, though they may be 

 easily and, I think, consistently traced back to their possible origin in 

 the Protozoa. 



It would be great presumption to say that even an approach to perfec- 

 tion had been attained in this attempted classification of a whole sub- 

 kingdom, of animals. Nevertheless in the preceding Table the relationships 

 existing amongst the members of that subkingdom are presented to the 

 eye at a single glance, and in a manner that would be quite unattainable 

 by systems maintaining the original creation of every so-called species, 

 and that in an order perhaps more easily described than understood. 



