LOWEST VERTEBRATE ANIMALS. 



2SS 



direct offspring of the present apes; neither do they 

 infer from these observations on the Ascidian larva that 

 vertebrate animals are descended from the Ascidians. 

 Their accordance much rather forces us to assume an 

 unknown primordial vertebrate family, springing from 

 some branch of the heterogeneous 

 division of the Annulosa. From 

 these diverged on one side the Tes- 

 tacea, who might perhaps be called 

 mischanced vertebrata, and on the 

 other the true vertebrate animals.'" 



The Amphioxus which lives in the 

 sand in shallow places on various 

 coasts, and is daily caught by thou- 

 sands at Messina for example, is five 

 or six centimetres in length, and is 

 compressed after the manner of a 

 fish, pointed at both ends, and semi- 

 transparent whilst alive. It pos- 

 sesses no trace of limbs, at the posterior end only a pair 

 of minute membranous margins, the indication of dorsal 

 and caudal fins, and is so simple in its internal structure 

 that it is usually, though inaccurately, termed a fish. Its 

 skeleton is limited to the noto-chord, and some minute 

 cartilaginous rods at the mouth and gills. It has no 

 brain, and, except a small ciliated sac, perhaps to be in- 

 terpreted as an olfactory organ, no sensory apparatus; 

 the heart is tubular. And thus between the lancelet and 

 other true fishes there exists so wide a difference that the 

 possibility remains open that the fishes passed through 

 some other course of development than phases like that 

 of the Amphioxus. 



FIG. 24. — Full-grown 

 Ascidian. 



