678 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
to, in which the unripe ova were of variable size, large and small, would probably have 
been retained until the end of winter or beginning of the year. The pelagic ova of this 
species are amongst the most abundant forms in and beyond the bay in March, April, 
and May. 
We have already spoken of the capsule as a zona radiata—a protective membrane of 
general occurrence in the ova of most diverse groups of Vertebrates. Thus in the Aves 
a zona radiata is present, though it does not persist; but at an early stage it dis- 
appears, and the egg leaves the ovarian follicle enveloped by another membrane which 
is distinguished as the vitellme membrane. This second membrane is exceedingly 
attenuate, so that it is difficult to distinguish it from the outermost layer of yolk-cells 
from which it is derived. The Leptilia possess also two membranes; but, unlike the 
birds, they are not both of vitelline origin, the outer, which is very thin, Ermer (No. 53, 
p. 418) declares to be a product of the follicular epithelium, and therefore chorionic ; but 
the inner is thicker, and vitelline in origin; and Ermer regards this as the zona radiata 
(his zona pellucida). The capsule in the Amphibia (Rana) is a remarkable structure, 
and would appear to be really a chorio-vitelline membrane, for the inner cells of the 
ovarian follicle form a layer very closely applied to the true vitelline membrane, 
and as the latter becomes continuously thinner the two layers are really inseparable, 
and form one layer, of which the outer stratum is chorionic, and the inner one is 
vitelline. 
In the Elasmobranchs a double layer is present, the outer being first formed, and 
regarded by Batrour as vitelline; while the inner one, equally of vitelline origin, he 
distinguished as the zona radiata. Both, however, atrophy as a rule before the egg 
leaves the follicle. In Cyclostomes (Petromyzon) two layers are described, an outer 
imperforate, and an inner perforated layer. The outer layer on contact with water 
swells up and forms a gelatinous coating by which the eggs adhere to external objects. 
In Myzxine, according to J. T. CunnincHAm’s researches, the thick capsule is a chorion, 
being developed along with its solid projecting processes from the follicular cells. 
Possibly a delicate vitelline membrane may be developed internal to the outer homo- 
geneous capsule, but this Mr CunnineHaAm was not able to decide (No. 46, p. 600). 
Notwithstanding that a double egg-membrane is so common, as indeed KOLLIKER long ago 
pointed out (No. 80, p. 84), yet in the Teleostei the recognition of a single layer of vitel- 
line origin accords best with the character of the capsule in general, in the mature ovum.* 
Certainly LEREBOULLET’s designation “ chorion” (No. 93, p. 459) is inappropriate ;+ nor 
does Kuprrer’s view, that the capsule in certain osseous fishes is double, like the 
Elasmobranchs, seem better justified. Kuprrer holds that, in the ease of Clupea 
* Dr Martin Barry affirmed that one membrane only envelops the ovum in fishes, no layer being formed 
external to the vitelline membrane (No. 21, p. 309). SotcEr also came to the same conclusion from an examination of 
Leuciscus rutilus (Arch. f. Mik. Anat., 1885). 
the primitive vitelline membrane separated from the vitellus ” (No. 93, p. 507). 
