CHAP. IV.] 



THE VOYAGE HOME. 



201 



the cg^ and embryo it is not a very favorable species for obser- 

 vation, had other conditions been favorable, we had all the ma- 

 terial for working out the earlier stages in the development of 

 the yonng very fully. The eggs, on being first placed in the 

 pouches, are spherical granular masses of a deej) orange color, 

 inclosed within a pliable vitelline membrane, which they en- 

 tirely fill. They become rapidly paler in color by the develop- 

 ment of the blastoderm ; they then increase in size probably by 

 the imbibition of water into the gastrula cavity ; and a whitish 





Fig. AQ.—Hemiaster Philippii. The arrangemeut of the eggs in one of the marsupial re- 

 cesses. Five times the natural size. 



spot Avith a slightly raised border indicates an opening which, I 

 have no reason to doubt, is the permanent mouth ; but of this 

 I can not be absolutely certain. The surface now assumes a 

 translucent appearance, and becomes deeply tinged with dark- 

 II.— 14 



