686 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
protoplasmic network, such as the reptilian ovum presents, or as Dr Scuuttz demonstrated 
(No. 144) in the Selachians. 
Little or no food-yolk makes its way into the germinal area, so that, as LEREBOULLET 
observes (No. 93, p. 485), it takes no part in the segmentation of the germ. Indeed, all 
evidence tends to prove that the deutoplasm is in an inert or quiescent state, and only 
passively contributes to embryonic development, being slowly incorporated by the active 
protoplasm of the blastodise in a mode which RypeR compares to the process of ingestion 
and assimilation in Amaba (No. 141, p. 557). 
When the eggs of Gadus morrhua are partially dried, the surface of the yolk shows 
a series of clear reticulations, which on re-immersion in water run together and disappear 
in the course of eight or ten minutes; such reticulations have, however, no connection 
with the later protoplasmic reticulation of the vitellus after epibolic extension of the 
blastoderm, and which is very noticeable in the cod, common dab (PI. V. figs. 3, 11), 
and others. HarckEL regards it as so much passive matter contained in a gastrula- 
cavity (No. 62); but in Teleosteans it plays a more important réle in later stages than 
that of supplying crude pabulum to the germ. Indeed, the germinal protoplasm 
Baprant holds to be solely transformed yolk—not a mere segregation of interfused 
germinal matter. The germ, he says, is formed “by endogenous development of cells at 
the expense of the yolk or primordial protoplasm;” but he repeats the error of Costr 
that the germinal area is never formed until after fecundation (No. 9). 
J. T. CUNNINGHAM, in a highly suggestive paper, observes that the yolk and germ are 
equally concerned in the processes of cleavage; segmentation in Teleosteans (as in 
Amphibians), dividing the ovum at the first stage of cleavage not equatorially, as E. 
vAN BrnebEN holds (No. 25), but meridionally into two similar halves, each with a cap of 
protoplasm and a mass of subjacent food-matter (No. 48). This view, however, gives 
to the crude deutoplasm an importance which cannot be accorded to it, even though 
cleavage as regards the yolk be merely potential and never fully achieved. 
The separation of the deutoplasmic mass into a segmenting blastoderm (Pl. XXII. 
fig. 1, bd), and an appended ball of pabulum (Jbid., y), is more complete in osseous fishes 
than in Elasmobranchs, and imparts to the yolk rather an accessory character than that 
of an active participator in the whole process of cleavage. 
That it contributes to the growing organism, and even buds off cells to build up part 
of the enteric tract, does not conflict with this view, which is supported by the fact that 
the yolk persists as a bulky appendage on the ventral surface of the young fish (PI. XIX. 
figs. 5, 7), until a late embryonic stage, being enclosed by the body-wall, and finally 
absorbed when the post-larval stage is reached. The passive réle attributed to the yolk 
Ryper would confine to the early stages, while later its function, he holds, is more 
important, since it becomes through the medium of the intermediary layer an active part 
of the ovum (No. 141, p. 569). 
But this view is not inconsistent with that here maintained, for if it serves as pabulum, 
this is really a part secondary to actual participation in blastodermic cleavage, and while 
