DEVELOPMENT OF THE GASTR^EA. 65 



animals, with the exception of the Protozoa. This highly 

 important fact justifies the inference in accordance with the 

 fundamental law of Biogeny, that the various ancestral 



FIG. 174. 



Fio. 179. 



FIG. 174 (A) Gastrula of a Zoophyte (Gastrophysema), Haeckel. 



FIG. 175. (B) Gastrula of a Worm (Arrow -worm, Sagitta). After Kowa- 

 levsky. 



FIG. 176. (C) Gastrula cf an Echinoderm (Star-fish, Uraster). After 

 Alexander Agassiz. 



FIG. 177._(D) Gastrula of an Arthropod (Primitive Crab, NaupUus). 



FIG. 178. (E) Gastrula of a Mollusc (Pond-snail, Limnoeus). After 

 Kail Rabl. 



FIG. 179._(F) Gastrula of a Vertebrate (Lancelet, Ampldoius) After 

 Kowalevskv. 



