THE STARFISH. 273 



II. Reproduction. Ova and sperms in immense num- 

 bers escape into the water, where fertilization takes place. 

 The resulting oosperm in its development passes through 

 the segmentation and gastrulation stages described for 

 the snail (pp. 158, 159), the irregularities there noted 

 being absent from the more typical development of the 

 starfish. The gastrula develops into curious larval forms 

 {Bipinnaria and Brachiolaria),for description of which the 

 student is referred to the larger text-books of zoology. 

 The larval forms are strictly bilateral. Were it not for 

 the persistent bilaterality of the water-vascular system, 

 the symmetry of the adult would be radial. The change 

 from larval to adult form is so great as to simulate meta- 

 morphosis. 



Lost parts, especially arms, are readily reproduced. 



Voluntary Motion and Sensation present no important 

 phases not already noted in preceding pages. 



The starfish is a representative of the large group 

 Echinodermata, a group which has no fresh-water rep- 

 resentative. Other echinoderms are crinoids, sea urchins, 

 and sea cucumbers. 



NEED. ZOOL. 18 



