DEVELOPMENT OF AMPHIURA SQtJAMATA. 147 



vitellins," which afterwards become the corpuscles of the body- 

 cavity. 



In Echinoids Prouho (15) describes the rudiment of the gland 

 as an " amas cellule allonge" at the side of the stone canal. 

 Cuenot (6), in Amphiura squamata, finds it arise as a thick- 

 ening of the wall of the axial sinus when the embryo has 

 attained a diameter of 700 fil Russo (16), in the same 

 form, as a cumulus of cells when the embryo has attained its 

 pentagonal form; and Apostolides (1) as a small swelling of 

 the stone canal. 



All these statements appear to me to be based on a few 

 casual observations ; but I cannot raise too strong a protest 

 against the superficial investigations on which the last three 

 writers have based a history of this organ. Since Cuenot 

 knows nothing of the origin of the sinuses, it is evident how 

 entirely wrong he must be. 



The case is very diflferent with the interesting observation 

 of Perrier (14) and Bury (2) on the dorsal organ of Crinoids. 

 This organ, in spite of Cuenot's objections, I regard as the 

 homologue of the ovoid gland. Cuenot^s first objection is that 

 the ampulla of the primitive stone canal in Crinoids disappears, 

 whereas in Ophiurids it surrounds the gland. As a matter of 

 fact it has precisely similar relations in both groups. His 

 second objection is that in Crinoids the genital rachis comes off 

 from the oral and not the aboral end of the gland, as in Ophiu- 

 rids. Taking Asterids for a moment, where the madreporite 

 has a dorsal position, we find that the genital rachis comes off 

 from not quite the aboral end, but there is a portion of the 

 gland beyond it, and this may correspond to the main mass of 

 the organ in Crinoids. The same thing is true of Ophiurids, 

 only here the madreporite is brought round to the ventral 

 side. 



As, however, to the general homology of the two organs the 

 observations of Bury and Perrier leave us in no doubt whatever. 

 According to the first observer the dorsal organ arises as a 

 cord of elongated cells ; since these lie in the concavity of a 

 prolongation of the right coelomic sac, which is crescentic in 



