DEVELOPMENT OF CRINOIDS. 



187 



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 

 stage of Antedon. 



The ovaries of Antedon open externally on the pinnules 

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

 nets of the male glands, and Thompson thinks that the 

 spermatic particles are " discharged by the thinning away 

 and 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) 



Fijsr. 129. Development of a Crinoid (Antedon'). A, morula; B, free larva, with 

 bands of cilia; C, young crinoid. After Wy ville-Tliompson. . 



from Wyville-Thompson's researches on Antedon rosaceus 

 (Fig. 130) of the European seas. In the first stage the egg 

 undergoes total segmentation (Fig. 129). 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 



