GERMINAL MEMBRANES. 219 
closely compared with the mouth of the polype and 
medusa, and the great central cavity of the sponge with 
the stomach of the others, of the canal system with 
the canals and cavities of the Ccelenterata,—then, in 
combination with the host of other facts, implying and 
supporting the doctrine of Descent, the inference is 
‘nevitable that in the Gastrula we.have a testimony 
of the consanguinity of the Spongiadze and Ccelen- 
terata. But this Gastrula reappears in the Holothuria ; 
hence in the Echinoderms, in the Sagitta, in the 
Ascidians, which will be more narrowly examined in 
the pedigree of the Vertebrata, and finally in the 
Lancelet; and we, therefore, hold ourselves justified 
in regarding this coincidence of the earliest states of 
development in different families, as the remnant of 
the common root, which in other families, as in the 
Articulata, for example, has been lost in the cur- 
tailment of development. The significance of the 
“germinal membranes” in the Vertebrata was recog- 
nized even by Pander, and in the suggestive works of 
v. Baer; the extension and application of this observa- 
tion to the whole animal kingdom, for which we are 
especially indebted to Kowalewsky, marks one of the 
greatest advances in the science of comparative de- 
velopment. 
The reader unacquainted with the detailed researches 
of our science, has already been called upon to observe 
that there are opponents of the theory of selection, such 
as Owen, who nevertheless accept the doctrine of Descent 
as incontestable. Even rejecting natural selection, the 
parallelism of Ontogenesis with Phylogenesis may also 
be brought into the natural connection maintained by 
