702 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



Lereboullet, Kupffer, Rieneck, and Oellacher all noticed the accumulation of 



globules under the disc in impregnated ova ; and Bambeke (who quotes them) says these 



indicate food-particles for nourishing the germ. Gerbe figures a crown of oil-globules 



around the periphery of the disc (No. 57, p. 330, pi. xii. figs. 3 and 4, b) ; while 



Oellacher speaks of his lenticular germinal mass as including a lower layer which 



imprisons many oil-spheres, and at times is seen to be separated by a distinct contour 



from the disc. Oellacher regards it as part of the blastodisc, and Bambeke likens 



it to his intermediary layer, though the subgerminal disc has been distinguished 



as a separate structure, neither to be confounded with the lower part of the germinal 



disc nor with the intermediary layer. Lereboullet indeed distinctly affirms that 



his mucous layer underlies, as a definite membrane, the blastoderm, while it rests 



upon the nutritive disc. Bambeke erroneously likens his intermediary layer to this 



stratum beneath Lereboullet's mucous layer in the trout (No. 20a). In Lereboullet's 



view, three distinct strata must be recognised at the animal pole — (1) the germinal 



disc proper, (2) the mucous or intermediary layer, and (3) the " disque huileux " or 



nutritive layer. The separation of the stratum underneath the disc into two layers has 



caused some confusion, and the distinction is perhaps unnecessary. It is readily seen 



that the lower portion of the intermediary layer will be more fully charged with oily 



spherules and granules from the yolk than the portion in apposition to the base of the 



disc, but it is needless to separate it as a distinct oily stratum. A subgerminal stratum 



is probably not absent in any Teleostean ovum, though less prominently seen in some 



(e.g., Gadoids and Pleuronectids) than in others (Esox and Gastrosteus), but the 



presence of a layer beneath the subgerminal stratum has been noted by very few 



observers. We cannot indeed regard Lereboullet's lowest (third) layer as separate from 



his mucous layer, which has been so generally recognised in Teleosteans. This single 



subgerminal layer, in whose lowest stratum oily spheres and granules are numerous, is the 



granular layer which Balfour speaks of, though in Elasmobranchs it consists chiefly of 



small yolk-spherules, and it is also Gotte's floor of the germinal cavity (the 



" Dotterzellen"). In Teleosteans it is continuous with the peripheral wall of protoplasm 



(His's "Keimwall") and the thin periblast beyond, originating in the same way, and 



persisting probably by continual renovation, the blastoderm thus feeding upon this 



finely granular layer. Kowalewsky regards the intermediary layer as a provisional organ 



(op. cit., 1886). We call by the name "subgerminal or nutritive disc" the disc-like 



stratum beneath the germ, and it embraces Lerebodllet's two layers — the mucous and 



the oily stratum ; it is the thin central part of Bambeke's intermediary layer ; it is 



Oellacher's inner layer, holding many oil-globules, of the " Eindenschicht ;" and although 



Oellacher speaks of it as more coarsely granular than the disc or layer above, yet 



it is derived from it. Oellacher rightly compares his lower layer to Lereboullet's 



mucous layer ; while Bambeke also correctly says that both are really his intermediary 



layer. 



We can therefore distinguish (with Bambeke) at the animal pole only two strata — 



