148 E. W. MACBEIDE. 



cross-section^ they may be regarded as peritoneal. This pro- 

 longation becomes divided longitudinally into five cavities, and 

 these form the beginning of the chambered organ. Later the- 

 axial organ grows up under the mesentery of the stomach with 

 an axial cord of Urkeimzellen. Bury finds that here, as in 

 Ophiurids (3), the ampulla of the stone canal represents an 

 anterior coelomic pouch. 



Perrier finds that the dorsal organ is a thickening of one of 

 the layers of the right peritoneal sac. When the dome of the 

 calyx opens it is ovoid, and formed of large pyriform cells with 

 a fibrous membrane. According to Perrier, diverticula from 

 secondary madreporic pores (entonnoirs vibratiles) form ves- 

 sels around the dorsal organ. If we accept Bury's view, and 

 make allowance for the great divergence of type between 

 Crinoids and Ophiurids, we might regard the sinuses of Ophiu- 

 rids as being equivalent to the chambered organ of Crinoids, 

 both being diverticula of the coelom. 



II. Genital Organs. — Hamann (8) describes a genital 

 rachis with Urkeimzellen in Asterids, Ophiurids, Echinoids, 

 and Crinoids. He proves that the genital tubes are outgrowths 

 of the rachis in Crinoids, Asterids, and Echinoids, and suspects it 

 in Ophiurids. Cuenot (5) has also asserted this origin for the 

 gonads in Asterids. He says a septum forms which closes the 

 sinus around the genital bud from the aboral sinus, and in this 

 the external opening is formed. Of the development of the 

 gonads in Ophiurids he merely asserts that it is precisely 

 similar; but I can assert that no such septum is formed in 

 them. Cuenot also asserts that the genital rachis is an out- 

 growth of the pseudo-heart in Asterids ; but this is a mere 

 guess, based on the similarity of the cells in both organs. 

 Between a stage where there is neither rachis nor aboral sinus, 

 and one in which both are completely formed, he finds no in- 

 termediate phase. His assertion that the ordinary cells of the 

 ovoid gland mature into Urkeimzellen finds no support from 

 my observations, which show that the portion of the gland 

 destined to form the primitive germ-cells is specialised from 

 the very first. 



