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. 176. 



Fig. 177. 



Pig. 178. 



Fig. 174 



Fig. 179, 



Fig. 174. — (A) Gastrnla of a Zoophyte (GastropTiysema), Haeckel. 

 Fig. 175. — {B) Gustrula of a Worm (Arrow-worm, Sagitta). After Kowa- 

 levsky. 



Fig. 176. — (C) GabLiuia jf au Echiuoderm (Star-fish, TJraster). After 

 Alexander Agassiz. 



Fig. 177. — (D) Gustrula of an Arthropod (Primitive Crab, Nauplius). 



Fig. 178.— (E) Gastrnla of a Mollusc (Pond-snail, Limnoeus). After , 

 Karl Rabl. 



Pig. I79,_(2r') Gastrnla of a Vertebrate (Lancelot, Amphioxus) After 

 Kowalevsky. 



