I A CHAPTER IN DARWINISM 33 



higher and more elaborate ancestors. These are certain 

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

 animals are found encrusting rocks, stones, and weeds 

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

 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 



