500 



COMPARATIVE ANATOMY 



CHAP. 



F. Cpinoidea (Fig. 395). 



In the Crinoids, a genital strand runs through the arms, branchings 

 with them, and entering into their last ramifications — the pinnulse. 

 While this genital strand, which is to be found even below the food 

 grooves of the tegmen calycis, remains as a rule infertile in the calyx 



and in the arms, in the 

 pinnules the g-erminal 

 cells which it contains, 

 give rise to the genital 

 cells. The genital strand 

 in the pinnulse becomes 

 a gonadial tube. 



On the position of the 

 genital strand cf. p. 414 

 and Fig. 356. It runs- 

 between tlie three brachial 

 sinuses of the body cavity 

 (between the dorsal canal 

 and the two ventral 

 canals), below the food 

 grooves of the arms. 



It is contained in a 

 special eoelomic sinus 

 (like the ring-like strand 

 and the genital strands 

 of the Asteroidea and the 

 Ophiiiroidea), to the wall 

 of which it is attached by 

 filaments of connective 

 tissue. 



The eoelomic sinus is continued on to the gonadial tubes of the 

 pinnulte and there becomes the genital sinus. 



The genital strand is at first solid, but at a later stage becomes a 

 hollow genital tube. This genital tube widens in the pinnules into 

 the gonadial tube, which, in mature piiniules, is filled either with eggs 

 or spermatozoa, these having their origin in the cells of the wall of the 

 gonadial tubes (the germinal epithelium). 



In a transverse section of the genital tubes of the arms, the wall 

 appears thickened at one part. This thickening is the section of a 

 ridge wliose cells seem to correspond with those of the germinal epi- 

 thelium of the gonadial tubes. 



It is very probable also, that after the ejection of the sexual pro- 

 ducts from the pinnules in Crinoids, the new formations of these pro- 

 ducts proceed from the germinal cells, which are pushed forward out 

 of the ridge of the genital tube into the pinnules. 



Fig. 3!15. — Transverse section through an ovarial 

 pinnule of a Crinoid, diiii,'raiuiiiati(_-. 1, nerve trunk of the 

 apical iiervo\is system in tlie joint of the pinnula ; '2, genital 

 .sinus ; 3, germinal eiiithelium of tlie gonadial racliis (genital 

 strand or tube) ; i and 9, sinuses of the brachial coelom ; 

 5, deeper longitudinal nerves of the pinnula ; 6, tentacle canal ; 

 7, radial canal of the water vascular system ; S, nerve ridge of 

 the superficial oral system ; 10, sacculus, see p. 400. 



