PEDIGREE OF VERTEBRATE ANIMALS. 25 1 



lutionary history of the individual. Only, if all verte- 

 brate animals testified their family connection by agree- 

 ing inter sc in the distribution of the germ as well as 

 in the fundamentally important organs, the spinal cord 

 and the vertebral column, this token of their descent 

 from inferior animals, which is unconditionally demanded 

 by the theory, seemed to be entirely wanting. In other 

 words, it seemed that in all vertebrate animals the 

 memory of their original derivation had been obliterated 

 by curtailed development (comp. p. 211). Thus the case 

 remained until Kowalewsky a few years ago studied the 

 development of the lancelet (Amphioxus), the lowest 

 vertebrate animal known, and showed that in this crea- 

 ture the typical phenomena of vertebrate development 



Fig. 22. Larva of the Lancelet after Kowalewsky. 



are preceded by the phases required by the theory. 

 We have already made acquaintance with this form of 

 development (p. 51, &c.), and we here again point out its 

 profound significance. It is only when the Amphioxus 

 has passed through the phase of the vibrating, sac-like 



