Till: II \ DB08PIBES A.ND 8PIBACLE3. BS 



Meek and Worthen 1 , writing aboul the same time as Billings, found that the 

 pinnules of Pentremites "arc cadi composed of a double series of alternatelj 

 arranged pieces and provided with a distinct longitudinal furrow along the inner 

 side, exactly corresponding to the ambulacra] furrows in the anus and pinnulse of 

 the typical Crinoids. It is therefore probable, as suggested by Dr. White, that these 

 furrows, in at least a portion of the pinnulse, were provided with receptacles for the 

 ova as in the true Crinoids." But the American authors do not commit themselves as 

 to the position of the genital glands in Pentremites. 



We do not believe for a moment that the pinnules merely contained receptacles 

 for ova which travelled down the ambulacra from the summit in order to mature 

 within the pinnules in the manner suggested by White ; but, on the other hand, we 

 see no very great improbability in the supposition that the ovaries themselves wen 

 situated in the pinnules. There are, however, one or two points which seem to us 

 to tell against this view. In the first place we much doubt whether the pinnules of 

 Blastoids can be regarded as homologous with those of a Crinoid. The latter are 

 repetitions of the arms on a small scale, with the same nervous, vascular, and 

 generative trunks, which last enlarge to form the fertile portions of the genital 

 glands. They receive branches of the ambulacra] or food-grooves, and thus form an 

 essential part of the apparatus for collecting the food particles in the water and 

 sending them down towards the mouth. But we doubt if there can have been any- 

 thing of this kind in the Blastoids, and there were certainly no lateral branches from 

 the water-vascular trunk within the lancet-plate into the pinnules. Furthermore the 

 apparently isolated ovaries of a Crinoid are in reality only the specially developed 

 and fertile portions of an extremely extensive genital gland, which has its centre in 

 the disc and sends ramifications along each arm beneath its ambulacral groove. ^ e 

 see no reason to believe that there was anything of this kind beneath the ambulacra 

 of a Blastoid where so much room is occupied by the lancet-plate and the hydrospire- 

 sacs ; while it is difficult to see how such a subambulacral genital rachis could have 

 given off branches into the cavities of the pinnules which arc situated more or less 

 above the ambulacrum. 



Among the recent Echinoderms it is the Ophiurids rather than the Crinoids which 

 appear to present structures corresponding to the hydrospire-sacs of a Blastoid. 

 Studer 2 showed in 1876 that the genital slits of Ophiurids lead into oval pouches 

 which lie at the sides of the arm-bases and have their walls strengthened by lime- 

 stone rods. The ovaries open into these pouches, which frequently contain young 

 Ophiurids undergoing a direct development. Studer therefore spoke of them as 



1 Proc. Acad. Nat. Sci. Philad. April 1869, p. 86. 



2 " Ober Echinodermen aus dem antarktdschen Meere und zwei ncuo Seeige] von den Papua-Inseln, 

 gesammelt auf der Raise S.M.S. Gazelle um die Erde.'* Uerliu Mouatsber. 1876, p. -162. 



m2 



