226 DAEWINISM STATED BT DARWIN HIMSELP. 



hermaphrodite, marine creatures permanently attached to 

 a support. They hardly appear like animals, and con- 

 sist of a simple, tough, leathery sack, with two small pro- 

 jecting orifices. They belong to the MoUuseoida of 

 Huxley — a lower division of the great kingdom of the 

 MoUusca ; but they have recently been placed by some 

 naturalists among the Vermes or worms. Their larvae 

 somewhat resemble tadpoles in shape, and have the power 

 of swimming freely about. M. Kovalevsky has lately ob- 

 served that the larvas of Ascidians are related to the Ver- 

 tebrata, in their manner of development, in the relative 

 position of the nervous system, and in possessing a struct- 

 ure closely like the chorda dorsalis of vertebrate animals ; 

 and in this he has been since confirmed by Professor 

 Kupffer. 



p " 160 Thus, if we may rely on embryology, ever 



° ' the safest guide in classification, it seems that 

 we have at last gained a clew to the source whence the 

 Vertebrata were derived. We should then be justified in 

 believing that at an extremely remote period a group of 

 animals existed, resembling in many respects the larvae of 

 our present Ascidians, which diverged into two great 

 branches — ^the one retrograding in development and pro- 

 ducing the present class of Ascidians, the other rising to 

 the crown and summit of the animal kingdom by giving 

 birth to the Vertebrata. 



FEOM NO BONE TO BACKBONE. 



Pa-'e 164 ^^^ '^°®* ancient progenitors in the king- 



° ' dom of the Vertebrata, at which we are able 



to obtain an obscure glance, apparently consisted of a 



group of marine animals, resembling the larvae of exist- 



