DEVELOPMENT OF THE GASTR^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 



FIG. 174. 



FIG. 179. 



FIG. 174. (A) Gastrnla of a Zoophyte (GastropJiysema), Haeckel. 



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

 levsky. 



FIG. 176. (C) Gastrula of au Echinoderm (Star-fish, Uraster). After 

 Alexander Agassiz. 



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



FIG. 178. (B) Gastrnla of a Mollusc (Pond- snail, Limnaeus). After 

 Karl Rabl. 



FIG. 179. (F) Gastrula of a Vertebrate (Lancelot, AmpMoxus) After 

 Kowalevsky. 



