672 PROFESSOR W. C. M‘INTOSH AND MR E. E, PRINCE ON 
in Gadus morrhua after treatment with osmic acid, but in both that and other species 
they were observed at the St Andrews Laboratory without preparation. As the time 
approaches for hatching, the capsule (¢.g., in Gadus aglefinus) often breaks up into 
flakes like the translucent chitinous secretions (tubes) of Annelids, The continued action 
of water and other causes seems to produce this physical change, so that the embryo is 
more readily extruded. 
We shall glance first at a few of the prominent features of demersal ova—the two 
most obvious points as compared with pelagic eggs being (1) the greater density of the 
zona radiata ; (2) the tendency to adhere together in masses by reason of the peculiar 
secretion which issues from the oviduct along with the ova. One of us has pointed out,* 
that in adhering together, eggs such as those of Cottus and Cyclopterus (vide Pl. 1. 
figs. 1-4) do so by limited areas of their surface, z.e., by facets, and thus the mass of 
ova is traversed by an intricate system of channels, which ensures more perfect aeration 
in the circumstances in which they are placed, e.g., in rock-pools. In the slow-running 
tanks of the Laboratory, however, these eggs develop less successfully than detached 
and floating forms, since the decomposition of a few frequently causes the death of the 
whole mass. 
Considerable variations are presented by the external surface of the zona radiata. 
Thus in Lepadogaster bimaculatus the capsule shows very evident punctures, and the 
ova, instead of being fixed to each other, are attached separately to shells, stones, and 
similar structures. Anarrhichas lupus, again, has the largest non-pelagic egg known 
to us. During the investigations for H.M. Trawling Commission in 1884, one of us 
had been familiar with the ovarian eggs of this form in their earlier stages, and in a 
morbid ovary some of the fully developed eggs were retained so late as the month of 
February, the spawning period apparently extending over the late autumnal or winter 
season, probably from October or November to December. It was not until the 16th of 
January 1886, however, that normal mature ova were obtained. A local trawler pro- 
cured in comparatively shallow water (5 to 6 fathoms) a large mass of them. These ova 
(Pl. XX. figs. 6, 7) are of a pale straw colour, with a slight opalescent hue. In shape 
they are more or less spherical, and measure 5°5 or 6 mm. in diameter. The zona 
radiata presents a comparatively smooth, though minutely punctured appearance 
(Pl. XX. fig. 8), and is very tough, so that the eggs, which are fixed to each other in 
the usual manner to facilitate aeration, can only be torn asunder with difficulty. In 
section (PI. I. fig. 25) a stratum (a), marked by a deep heematoxylin-stain, separates an 
outer thicker from an inner thinner portion of the zona radiata. Fine striations or pore- 
canals are also seen traversing the entire thickness of the capsule. A single large oil- 
globule 1°75 mm. in diameter occurs in each ovum. This, as usual, constantly passes to 
the upper pole, just as the oil-globule does in pelagic eggs. Only a single unimpregnated 
egg was available for the demonstration of the early condition. In some unhealthy 
or dying eggs a number of very small oil-globules were seen clustering round the edge 
* M‘Inrosu, Nature, June 1886. 
