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 (e.g., in Gadus ceglejinus) 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 PI. I. 

 figs. 1-4) do so by limited areas of their surface, i.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 bimacidatus 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 

 (PI. 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 hsematoxylin-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'Intosh, Nature, June 1886. 



