REVIEWS AND BOOK NOTICES. 681 
work done in this direction may, without fear of contradiction, be 
cited that of Kowalevsky ; in showing the identity of development 
of Amphioxus and of the Ascidians, he closed with a single stroke 
defended in two essays of a high philosophic import. Haec 
Annals and Magazine of Natural History, under the title ; “On 
the Primitive Cell-layers of the Embryo as the Basis of the Genea- 
logical Classification of Animals” by my friend E. Ray Lankester. 
All the pluricellular animals, in which the development begins 
by the segmentation of the cell-egg, pass through in the course of 
their evolution a similar embryonic form, that of a sac whose thin 
zation; that the endoderm has in all the same morphological 
value; that the primordial digestive cavity of vertebrates, and 
tof all other types of organization have the same anatomical 
= 
and Von Baer. Finally, we can infer the existence at a geologi 
“heir external characters, have been the common source of verte- 
brates, arthropods, mollusks, echinoderms, worms and zoophytes ; 
they constitute the very numerous group of Gastræades (Haeckel). 
