DEGENERA TION. 



41 



My object in the next place is to show that the 

 structure and life-history of these Ascidians may 

 be best explained on the hypothesis that they are 

 instances of degeneration ; that they are the modified 

 descendants of animals of higher, that is more 

 elaborate structure, and in fact are decreneratc 



Fig. 15. — Anatomy of an Ascidian (Phallusia). At the top is the mouth, to the right 

 the orifice of the cloaca. In the cloaca lies an egg, and above it the oblong nerve 

 ganglion. The perforated pharynx follows the mouth and leads to the bent in- 

 testine which is seen to open into the cloaca. The space around the curved 

 intestine is the body-cavity ; in it are seen oval bodies, the eggs, and quite at the 

 lower end the curved heart. The root-like processes at the base serve to fi.v the 

 Ascidian to stones, shells, or weed. 



Vertebrata, standing in the same relation to fishes, 

 frogs, and men, as do the barnacles to shrimps, 

 crabs, and lobsters. 



The young of some, but by no means of all these 



