PliOPAaATlON OF CBllTAIN ECmNODEKMS. 69 



the paired ambulacra are greatly expanded and lengthened, and 

 thinned out and depressed so as to form four deep, thin-walled, 

 oval cups sinking into and encroaching upon the cavity of the test 

 (fig. 8). The ovarial openings are, of course, opposite the inter- 



Hemiaster, sp. Apical half of the test of a female example, from within. 

 Natural size. 

 radial areas ; but the spines are so arranged that a kind of covered 

 passage leads from the opening into the marsupium ; and along this 

 passage the eggs, which are remarkably large, upwards of a milli- 

 metre in diameter when they leave the ovary, are passed, and are 

 arranged very regularly in rows on the floor of the pouch, each 

 egg being, kept in its place by two or three short spines which 

 bend over it (fig. 9). 



Among the very many examples of this Semiaster which we 

 dredged in Accessible Bay, and afterwards in Cascade Harbour, 

 Kerguelen, there were young in all stages in the breeding-pouches ; 

 and although from the large size and the opacity of the egg and 

 embryo it is not a very favourable species for observation, had 

 other conditions been favourable we had all the material for 

 working out the earlier stages in the development of the young 

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

 spherical granular masses of a deep orange colour, enclosed within 

 a pliable vitelline membrane, which they entirely fill. They become 

 rapidly paler in colour by the development of the blastoderm ; and 

 they increase in size probably by the imbibition of water into the 



