LOWEST VERTEBRATE ANIMALS. 255 



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. 75 



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- F1G 

 transparent whilst alive. It possesses 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 interpreted 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. 



