THE DEVRLOPMENT OP ASTERTNA GIBBOSA. 225 



of the Asterid and Crinoid to their common ancestor were 

 designed for me by my friend and colleague Mr. J. J. Lister, 

 of St. John's : in their present form they were drawn for me by 

 a lady friend. 



The Development of the Larva. 



The eggs are laid by the parent on the under surface of 

 stonesj to which they adhere by means of their vitelline 

 membrane. I have never discovered a male, though Ludwig 

 says that the male twists his arms round the female whilst she 

 is depositing her ova, and then pours out his spermatozoa 

 upon them ; it is quite certain that in the English Channel, 

 at any rate, isolated females will lay eggs which develop with 

 perfect regularity up to the conclusion of the metamorphosis. 

 Cuenot (4) says that young females of a certain size develop 

 spermatozoa in their ovaries — a statement I have not been able 

 to verify. It may, indeed, be said that Ludwig's statement that 

 a kind of sexual congress takes place, Cuenot's observations, 

 and the experience of the authorities of the Jersey Biological 

 Station are irreconcilable, and that the whole subject demands 

 renewed investigation. 



The eggs are larger than those of most other Echinoderms; 

 they are about "5 mm. in diameter. This is a result of the 

 yolk which they contain, and which gives them their bright 

 orange colour. This yolk is so uniformly distributed, however, 

 that it does not alter the type of segmentation, which is total 

 and regular. The blastomeres, in consequence of their larger 

 size, are more closely packed than is usual amongst Echino- 

 derms ; they are wedged into the interspaces between their 

 neighbours, and so the strict "radial"^ type of segmentation 

 characteristic of the group is no longer maintained. 



The result of segmentation is a hollow blastosphere or 

 blastula, which on the second day of development becomes 

 converted into a gastrula by embolic invagination. The embryo 



1 For a discussion of the different types of regular segmentation see " Tlie 

 Cell-lineage of Nereis," by Prof. E. B. Wilson, 'Journal of Morphology,' 

 vol. vi. 



