GERMINAL MEMBRANES. 



219 



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 in- 

 evitable that in the Gastrula we have a testimony of the 

 consanguinity of the Spongiadse and Ccelenterata. 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, there- 

 fore, hold ourselves justified in regarding this coinci- 

 dence 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 curtailment of development. The significance 

 of the " germinal membranes " in the Vertebrata was 

 recognized 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 develop- 

 ment. 



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 

 parellelism of Ontogenesis with Phylogenesis may also 

 be brought into the natural connection maintained by 

 us, on the assumption of an unnatural or supernatural 

 guidance which converts this apparently natural unity 



