668 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



living egg, especially in the case of pelagic ova, and also to a certain extent in demersal 

 forms. This translucency is due to the disappearance of the granules in the yolk of the 

 ovarian egg when ripe. Sometimes, however, eggs which are not perfectly mature, i.e., 

 lack the translucency of the ripe ovum, may yet be fertilised, and their embryos in due 

 time liberated. This was frequently the case with imperfectly ripe eggs of T. gurnardus, 

 which, though presenting slight opacity, were successfully hatched. Occasionally eggs of 

 the species just named exhibit a remarkable pinkish or reddish coloration, the oil-globule 

 being of a dark tint (PI. XVI. fig. 10). The cause or meaning of this abnormal appear- 

 ance is undecided; the eggs, of course, were not fertilised, and did not develop ; indeed, 

 this coloration has only been seen in dead eggs. Pelagic eggs, when dead or unhealthy, 

 show a great increase in the perivitelline space, and sink to the bottom of the tanks. 

 Sometimes living eggs, from various causes, such as a change in the specific gravity of 

 the water, sink, this being frequently the case with T. gurnardus ; yet when the water 

 is violently stirred, or when removed from still water for examination, and then emptied 

 into the tanks, they again often assume their buoyancy. This may be due to the dis- 

 engagement of particles of foreign matter, such as sand, though this is not always 

 evident. The eggs of Molva vulgaris (PI. I. fig. 10) are less buoyant than some other 

 Gadoids, e.g., Gadus morrhua and G. ceglejinus, and sometimes, though living, sink to 

 the bottom in quiescent water, yet successfully develop. The ova of the ling are indeed 

 more delicate, and more susceptible to unfavourable conditions than those of the cod and 

 haddock. The addition of spirit to a vessel containing them causes them to rush to the 

 side of the vessel, and cling to it with tenacity. The hardy character of certain pelagic 

 eggs and their vitalit} 7 was shown in many cases at the Laboratory. No difficulty was 

 found in developing eggs fertilised at sea and conveyed long distances, in some cases after 

 travelling in earthenware jars for three or four days. Eggs of the cod contained in such 

 jars, three-fourths filled with sea- water, reached the Laboratory on the fourth day after 

 fertilisation, and though most of the eggs had sunk to the bottom, and the w T ater was 

 offensive with putrid matter — Infusoria, Bacteria, and Spirilla being abundant, yet many 

 of the eggs still floated at the surface, and the hearts of the embryos pulsated regularly. 

 The effect of cold is to retard development, but is not detrimental unless extreme. In 

 one instance a series of the eggs of the haddock were floating buoyantly in the tanks at 

 6 p.m., but next morning the glass vessel was covered with a coating of ice, on breaking 

 which most of the eggs fell to the bottom, and in these the yolk and germinal area were 

 found to be much shrunken and corrugated, leaving a wide space round the vitelline 

 mass. A few only survived, these having apparently remained under the trickle of the 

 supply pipe.* That pelagic eggs float in sea water, while they sink in fresh water, or in 

 sea water having an admixture of fresh, Professor Baird has shown to be due to the 

 fact that their specific gravity is about 1'020 or l*025.t 



* Vide Nature, June 1886. 



t Of this floating property, the oldest fishermen, Baird adds, had not the slightest idea ; they thought " that the 

 females deposited their eggs on the rocks, where they were visited and impregnated by the males They had 



