DEVELOPMENT OF THE GASTK^A. 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 



PIG. 174. 



FIG. 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 of an Echinoderm (Star-fish, Uraster). After 

 Alexander Agassiz. 



FIG. 177. (D) Gastrala of an Arthropod (Primitive Crab, Nauplius). 



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

 Karl Rabl. 



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

 Kowalevsky. 



VOL. II. F 



