DEVELOPMENTAL HISTORY OF THE MOLLUSCA. 45 
In this phase it is, as far as the eye assisted by the microscope can ascertain, in the 
Jresh state, a homogeneous transparent viscid body, devoid of any special membrane to 
protect its surface, but retaining its ovoid shape, owing to the greater density of its 
superficial layer of substance. In this phase no marking of the surface to indicate the 
former sites of the capsular ridges *, no trace of a germinal vesicle, can be seen. I have 
not represented the egg at this period in the Plates; for it would be purely negative as 
seen by transmitted light, a simple ovoid outline and nothing more. I have traced the 
germinal vesicle up to the condition of eggs, such as Plate 11. fig. 8, but not beyond. 
I agree with K6.uiKker that it disappears; but I have not traced the mode of its 
disappearance. It is not unlikely that it is absorbed at the same time as are the 
capsular ridges. 
The homogeneous unfertilized egg which now lies in the upper portion of the ovi- 
duct is not, however, devoid of all differentiation of structure. 
In the first place, when hardened in absolute alcohol, cut in sections and stained with 
carmine, a stratified arrangement of the substance of the egg becomes obvious (Plate 11. 
fig. 12), as many as four bands of differing intensity of staining being demonstrable. 
These apparently indicate differing density of the successive layers of yelk-substance, 
and are possibly connected with the successive modes of yelk-nutrition which we have 
distinguished. But, in addition to this, on breaking up a fresh specimen of an egg 
belonging to this phase, and allowing the yelk to spread out on a glass slip, covering 
and examining with a power of 600 diameters, it becomes obvious that the yelk is not 
_ in its nature homogeneous. In this case (Plate 12. fig. 24), and at later stages, a 
perfectly definite structure uniformly spread through the mass can be observed. It 
is possible to distinguish highly refringent, irregular, somewhat botryoidal masses and 
interspaces occupied by a less dense material, probably a liquid, the denser masses being 
viscous solids. The liquid must be relatively very small in amount; for it is only 
when carefully spread out that the yelk-particles become obvious, and with the highest 
powers they are seen as of a greenish tint, whilst the interspaces are pink}. The 
botryoidal denser matter must without doubt be directly traced to the metamorphosed 
cells thrown in from the inner capsular membrane. The forms and sizes of the masses 
assumed by this material when spread out are too indefinite to admit of measurements, 
but may be best judged of by the figures. It is necessary again to observe that, in the 
undisturbed egg, the particles are so densely packed that the mass has the appearance 
of being quite homogeneous. It is not until the particles are allowed to move on one 
another a little that the granular or botryoidal structure of the yelk becomes obyious. 
* Such markings are sometimes to be seen. 
T These colours are of course only due to the optical defects of high-power objectives. 
