216 Ovarian Egg of the SaccuUnm. [''f^nllK'^m^lm. 
This first phase is soon succeeded by others which reveal to us 
the part to be played by the two vesicles. Both these vesicles 
speedily become enveloped by fine globules, which make their 
appearance in succession. But whilst round one of the vesicles 
the globules remain very small, preserve nearly the same volume, 
and seem to have but a limited multiplication, we see them round 
the other vesicle present very diflPerent sizes, increase by small 
degrees, and become more abundant as the ovule is nearer to 
maturity. 
That lobe of the egg in which the increase in number and 
volume of the primitive elements takes place, necessarily undergoes 
relative modifications. It grows larger to provide room for the mate- 
rials which multiply in it, in the same way as the vitelline membrane 
of the bird's egg grows as the yolk becomes developed, and ends 
by assuming so great a predominance, that the other lobe, whose 
development has to a certain extent remained stationary, represents 
only a small eminence on one of the poles of the ovule like that 
which is produced in the egg of the osseous fishes as a consequence 
of the condensation of the vitellus. 
Such is the appearance presented by the mature ovule of the 
Sacculinse. As to its organization, it only difiers from that of the 
very smaU ovules, by the intervention of two distinct elements in un- 
equal proportions. The predominating element, formed of a mass 
of large and small globules, in the midst of which one of these 
primitive vesicles is always to be seen, is without doubt the analogue 
of the yolk of the bird's egg, that is to say, the matter destined to 
the nutrition of the future embryo; while the circumscribed disc, 
situated at the periphery of the egg, and composed of very minute 
granules grouped round the other primitive vesicle, manifestly 
represents the cicatricule of birds, that is to say, the essential and 
fundamental portion of the egg, that of which the materials will 
be directly employed in the formation of the new being. The 
study of the ovules of the Sacculinse, then, shows us the meaning 
of the two vesicles which are contained in the eggs of certain 
species. We may even say that the demonstration is here complete, 
for we follow the phenomenon through all its phases. One of these 
vesicles is the centre of the formation of the germinative element, 
and ought to preserve the name of germinative vesicle, under which 
it is now known ; the other is only the centre of formation of the 
nutritive element.* 
* * Comptes Hendus,' Feb. 22. 
