ioo THE EVOLUTIONIST AT LARGE. 



original ancestor, the very earliest vertebrate 

 of all, must have been a transparent creature, 

 and therefore comparatively indifferent as to 

 the part of his body in which his eye hap- 

 pened to be placed. In after ages, however, 

 as vertebrates generally got to have thicker 

 skulls and tougher skins, the eye-bearing part 

 of the brain had to grow outward, and so 

 reach the light on the surface of the body : a 

 thing which actually happens to all birds, 

 beasts, and reptiles in the course of their 

 embryonic development So that in this 

 respect the ascidian larva is nearer to the 

 original type than the tadpole or any other 

 existing animal. 



The ascidian, however, in mature life, has 

 grown degraded and fallen from his high 

 estate, owing to his bad habit of rooting 

 himself to a rock and there settling down 

 into a mere sedentary swallower of passing 

 morsels a blind, handless. footless, and 

 degenerate thing. In his later shape he is 

 but a sack fixed to a stone, and with all his 



