DEVELOPMENT OF CBINOIDS. 



105 



relations as in the unstalked Crinoids {Antedon and Actin- 

 ometra), only they are on a simpler plan, there being a 

 ■close similarity between Rhizocrinus and the pentacrinoid 

 ^tage of Antedon. 



• The ovaries of Antedon open externally on the pinnules 

 •of the arms, while there is no special opening for the prod- 

 ucts of the male glands, and Thompson thinks that the 

 spermatic particles are " discharged by the thinning away 

 iind dehiscence of the integument." The ripe eggs hang 

 for three or four days from the opening like a bunch of 

 grapes, and it is during this time that they are fertilized. 

 The following account is taken (sometimes word for word) 



Pig. 66.— Development of a Crinoid (.Antedon). A, morala; B, free larva, witli 

 tands of tUia; C, young crinoid.— After Wy ville-Thompson. 



from Wyville-Thompson's researches on Antedon rosaceus 

 (Fig. 67) of the European seas. In the first stage the egg 

 undergoes total segmentation (Fig. 6(3). A represents the 

 egg with four nucleated cells, an early phase of the mul- 

 berry or morula stage. After the process of segmentation 

 of the yolk is finished, the cells become fused together into 

 a mass of indifferent protoplasm, with no trace of organiza- 

 tion, but with a few fat cells in the centre. This pro- 

 toplasmic layer becomes converted into an oval embryo, 

 whose surface is uniformly ciliated. The mouth is formed 

 "with the large cilia around it before the embryo leaves the 



