PHYLOGENY. 



81 



of the body, connecting several ganglia, (with some 

 exceptions where the ganglia are fused or wanting). 

 There is no internal skeleton. In the last and highest 

 branch, that of the Vertebrata, the body is longitudi- 

 nal and is segmented. It has a longitudinal nervous 

 axis on the superior middle line, which is supported 

 below by an axis of resistant material, usually bone, 

 which forms the axis of an internal skeleton. Seg- 

 mented limbs are present. 



The lines of descent of these branches indicated by 

 embryology are as follows : 



Vertebrata. 



Arthropoda. 



Mollusca. 



. 



Echinoderma_ta. 

 Porifera. 



'ermes< 



Coelenterata. 



Catallacta. 



Protozoa. 



The above series present a history which is, on the 

 whole, very different from that already described as 

 characterizing the vegetable kingdom. Between the 

 first and last terms of the series, there is exhibited a 

 great progressive advance in all the higher features of 

 life. These are mobility, and such control over the 

 environment as it gives ; and sensibility, through the 

 development of a nervous system, which gives control 

 over the movements. The highest development is 

 that of mental characteristics, as emotions and intelli- 

 gence, which are especially seen in the higher Verte- 

 brata, 



