34 



EVOLUTION AND ANIMAL LIFE 



FIG. 21. A group of stalked one-celled 

 animals, Carchesium, sp. (Adapted from 

 Davenport, from a photograph of the liv- 

 ing animals.) 



grouped into two regions and 

 the appendages limited to 

 the anterior one of these 

 two. The Myriapods, which 

 are also Arthropods, have a 

 structure more in conformity 

 with what may be called the 

 racial or typical plan for the 

 whole phylum; that is, the 

 body is made up of a se'ries 

 of many successive similar 

 segments, each segment bear- 

 ing a pair of jointed ap- 

 pendages. In -that general 

 line of descent to which 

 man belongs, and which is 

 distinguished by the name 

 of the phylum Chordata, 

 there are of course various 

 subordinate lines which we 

 recognize under the names 



further the general classifi- 

 cation of animals into phy- 

 la. Nor need we explain 

 in any detail the structural 

 types or fundamental struc- 

 tural plans which distin- 

 guish the various principal 

 lines of descent in the 

 animal kingdom. 



Branching out from each 

 of the principal lines are 

 hosts of subordinate lines. 

 Some of the Arthropods, as 

 the insects, have their body 

 segments grouped into three 

 regions and their jointed 

 appendages confined to the 

 anterior two of these re- 

 gions. Others, as the spiders, 

 have the body segments 



B 



FIG. 22. Gonium pectorale, a colonial pro- 

 tozoon: A, seen from above; B, seen from 

 the side. (After Stein.) 



