PEDIGREE OF VERTEBRATE ANIMALS. 251 
lutionary history of the individual. Only, if all verte- 
brate animals testified their family connection by agree- 
ing wzter se 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 ycars 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 
