GENERAL REMARKS ON THE EGGS OF MARINE FISHES. 19 



floating, on arrival, at the surface of the water. On transferring 

 the eggs of the cod to a larger jar and turning on a tap of sea 

 water they in a few minutes went to the bottom, the impure 

 sea water on these occasions proving speedily fatal. The addi- 

 tion of a small quantity of methylated spirit in the same way 

 sends all the eggs and embryos to the bottom. Sars, indeed, 

 mentions that if the eggs of the cod are placed in fresh water 

 they sink and never again rise. They are killed just as a 

 newly hatched salmon is killed, though somewhat more slowly, 

 by immersion in sea water. Sars thinks that even a fall of rain 

 might affect the floating of the eggs in the sea, but this is 

 unlikely, since as a rule the eggs are not, in our seas at least, 

 found quite at the surface. Occasionally the diminished density 

 of shore water suffices to send the eggs captured in the open 

 sea to the bottom of a vessel, but they are by no means killed. 

 The attachment of fine particles of mud and sand in the same 

 way carries the eggs downward, and often proves disastrous to 

 them. 



More than once the eggs of the haddock and other fishes 

 have been brought under notice as lying on the bottom of a 

 vessel, and therefore held as proof that they did not float. But 

 in every such case of pelagic eggs they were either dead or dying, 

 unripe, and often unfertilized. If in removing eggs from a fish 

 too much pressure is applied, unripe eggs escape ; and they 

 either sink or float ambiguously according to the stage of 

 development. Unless this fact is borne in mind disappoint- 

 ment naturally ensues, especially in the case of those who have 

 brought them from deep-sea fishing to vindicate their state- 

 ments. No one ever asserted that dead eggs floated. It is the 

 ripe and living eggs that are so buoyant. 



While thus, if care be exercised, there is no great difficulty 

 in transmitting the pelagic eggs 1 of marine fishes great dis- 

 tances immediately after fertilization, it is, in critical cases, 

 better to wait till the embryo is outlined before subjecting 

 them to such vicissitudes. The mortality is by this method 



1 In stoneware jars tied over with cheese-cloth, and comparatively few eggs 

 in each vessel. 



22 



