DEVELOPMENT OF OVA OF BIRD. 579 
to that of the parent, than we see in any other animals. The 
appearance of the ovary of the Fowl in process of laying is 
shown in fig. 314; its surface is rendered uneven or knobby 
Fig. 314.— Ovary of the Fowl, with ova in various stages of development: 
a, mature ovum within its calyx, which is about to rupture along the non-vascular 
streak b b ; c c, less advanced ova ; d , a calyx from which the ovum has escaped ; 
e, still younger ova. 
by the protrusion of the ova in various stages of enlargement, 
those which are most mature (a, c) forming pear-shaped 
projections which only hang-on by a narrow stalk ; but each 
ovum is still included within an extension of the fibrous sub¬ 
stance of the ovary (fig. 302), termed the calyx, through which 
blood-vessels are conveyed over its surface; and when the 
ovum escapes by the rupture of this, along a line (b) from 
which the vessels have previously retreated, the calyx remains 
as an open cup ( d ). The ovarium of such Mammals as pro¬ 
duce several young at once, presents a corresponding appear¬ 
ance as each set of ova is approaching maturity; save that, as 
the mass of yolk is comparatively small (no “food-yolk” being 
provided), the ova do not project so much from its surface. 
In Fishes, on the other hand, we find an enormous number 
of ova produced at once ; the whole ovarium, when they are 
approaching maturity, being so crowded witfy them that its 
p p 2 
