I A CHAPTER IN DARWINISM 33 



higher and more elaborate ancestors. These are certain 

 marine animals, the Ascidians, or sea-squirts. These 

 animals are found encrusting rocks, stones, and weeds 

 on the sea-bottom. Sometimes they are solitary (Fig. 

 13), but many of them produce buds, like plants, and 

 so form compound masses or sheets of individuals all 

 connected and continuous with one another, like the 

 buds on a creeping plant (Fig. 14). 



We will examine one of the simple forms a tough 

 mass like a leather bottle with two openings ; water is 

 continually passing in at the one and out at the other 

 of these apertures. If we remove the leathery outer 

 case (Fig. 15), we find that there is a soft creature 

 within which has the following parts : Leading from 

 the mouth a great throat, followed by an intestine. 

 The throat is perforated by innumerable slits, through 

 which the water passes into a chamber the cloaca : 

 in passing, the water aerates the blood which circulates 

 in the framework of the slits. The intestine takes a 

 sharp bend, which causes it to open also into the 

 cloaca. Between the orifice of the mouth and of the 

 cloaca there is a nerve-ganglion. 



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 modi- 

 fied descendants of animals of higher, that is, more 

 elaborate structure, and in fact are degenerate Verte- 

 brata, standing in the same relation to fishes, 

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

 and lobsters. 



D 



