MADE AT THE PLYMOUTH LABORATORY. 267 
In my previous paper I described the condition of the spent 
ovary of the plaice, as seen when microscopically examined in the 
fresh condition, and expressed the conclusion that all the unripe 
eggs containing yolk remaining in the ovary were destined to 
degenerate and be absorbed. The chief characteristic of sections 
of a spent ovary consists in the number of empty follicles seen. 
These are the collapsed receptacles in which the ripe ova were 
developed, and from which they have been expelled. The mode of 
expulsion is constant and of some importance. The follicle bursts 
at the surface of the germinal tissue, the egg therefore escaping 
through a rupture of the so-called germinal epithelium. When this 
takes place the wall of the follicle becomes continuous with the 
external covering of the germinal tissue,—that is to say, with the 
germinal epithelium and the connective tissue which supports it. 
Such an empty follicle corresponds with what is called a corpus 
luteum in the mammalian ovary. In the fish its walls are thick, 
and contain many blood-vessels: it may be regarded as an elastic 
membrane, which, having been stretched round the large ripe ege, 
becomes thickened and contracted when the latter escapes. In the 
cavity of the follicle are always seen the separated and broken 
follicular cells, but there are indications of cells on the surface of 
the interior of the follicle, so that perhaps not the whole of the 
follicular epithelium perishes. The appearance of the empty follicles, 
opening by an aperture at the surface of the germinal tissue, and 
of their walls, continuous with the membrane at the surface, strongly 
suggests the idea that a follicle is simply a pocket formed in the 
germinal membrane and temporarily constricted off from it, being 
restored to it again when the mature egg is expelled. But whether 
the wall of the follicle becomes again a part of the germinal 
membrane and begins again to produce new ova, or whether it is 
gradually absorbed, is a question I am unable to answer at present. 
In the larger of the young yolkless ova in the spent ovary the 
vitelline nucleus is present. 
I have now to describe some observations on ovaries in which 
the history of the ova presents considerable differences from that 
which is characteristic of flat fishes and other fishes with pelagic 
ova. 
Henneguy,* in a recent paper on the vitelline nucleus, states that 
among all the Teleosteans whose ova he examined, those of the pipe- 
fish (Syngnathus acus) gave him the most interesting facts. These 
facts are described thus :—There are four stages of the develop- 
ment of the vitelline body: (1) The smallest ova have no vitelline 
* Le corps vitellin de Balbianit dans Veuf des Vertébrés, Journ, de Anat. et de la 
Physiol., No. 1, 1893, 
