DEVELOPMENT OF CRINOIDS. 187 
relations as in the unstalked Crinoids (Aztedon 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- 
ucts 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) 
Fig.129.—Development of a Crinoid (Antedon). A, morula; B, free larva, with 
bands of cilia; C, young crinoid.—After Wy ville-Thompson, 
trom 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 
