24 SALMOKID^ OF BRITAIN. 



preventing the development of the ova, or should they be present in the ovaries 

 by arresting, or retarding their further increase in size. 



Among these fishes— at least in the salmon — the female is normally one year 

 later than the male in attaining to a breeding condition, -while it has been 

 observed at Howietoun that the extrusion of milt or ova may be retarded even 

 for several weeks in ripe fish if placed in a box having smooth sides, and through 

 -which a sufficient stream of water passes. The eggs are ovoid, or nearly circular, 

 elastic bodies of a clear white, pink, or coral colour, the outer coat, which is 

 porons, possessing much toughness and elasticity, properties most important to 

 its future existence in the localities where it is naturally deposited, or in the 

 subsequent movements which it may have to go through. On the surface of each 

 egg may be seen a microscopic orifice (looking like a healed ulcer on the cornea 

 of the human eye), termed the micropyle, which allows the entrance of the 

 spermatozoa, without which it would remain unfertilized, and consequently 

 barren. 



The eggs, as extruded, are soft, but rapidly absorb water which fills up the 

 interspace between the outer shell and its delicate inner lining, and as soon as 

 this period of absorption has passed by, which has been considered not to exceed 

 thirty minutes in trout eggs,* it is impossible for the ova to be fertilized. Should 

 these eggs have milt added to them in the water, it is evident that unless 

 fertilization rapidly occurs the spermatozoa may have perished. On the other 

 hand, should eggs be obtained from a fish and expressed into a dry pan (or one 

 into which no water has been placed), and milt added in their own fluid and 

 thus stirred up among the ova, the supposition would be .that these organisms 

 would more likely be active when thus employed than in water which rapidly 

 destroys their vitality. And fish-culturists have found in practice that this which 

 is termed the " dry process " is far more successful than when water is first used 

 or the " moist process " employed. 



A difference of opinion respecting the persistent or variable size of the eggs of 

 SalmonidsB appears to prevail, which could not continue to exist if contending 

 parties would take the trouble to measure them when freshly removed from the 

 parent fish, or as lying in the hatching-troughs. For they do not increase in size 

 during the process of incubation, although such as die in fresh water become 

 sodden, white, and somewhat distended.f While the observations recorded below 

 and which have been since made conclusively show that the eggs of these fishes 



* Mr. James Annin {American Fish Cultwral Association, 1885, page 110) observed that during 

 the past -winter he had made an experiment -with eggs taken from a fine healthy brook trout, 

 Salmo fontinalis, impregnated by a number of good males of the same species. First 350 eggs 

 had milt added, and then -washed off as quickly as possible, and 45 seconds after extrusion 

 they -were placed on the trays in the hatching troughs. Next 360 more eggs -were expressed from 

 the same fish, and -were allo-wed to stand three minutes before the milt -was washed ofi. The 

 rest of the eggs from this fish, 335 in number, -were allo-wed to remain thirty minutes in the 

 spa-wning pan. The three lots -were carefully placed on the trays, the bad ones -were daily 

 removed until the eyes became visible, -when the results -were as follo-ws : — 01 the first lot only 

 six were impregnated, or about one in 58 ; of the second lot 31, or about 1 in 11 ; and of the last 

 lot about 1 in 1^. Max von dem Borne observed {0-U. Fisclierei-Zeitung, Vienna, 1880) that he 

 had sent salmon eggs and milt from Basle mixed together in a hog's bladder without the addition 

 of water. The journey lasted three days, and the temperature was high, in spite of which they 

 arrived in good condition : while some eggs treated in the ordinary manner, and similarly sent, 

 were almost all received dead. 



jl Harmer in 1767 {Transactions of the Royal Society, " On the Fecundity of Fishes ") gave 

 a table showing the number of eggs which he had observed in certain forms of fishes, among 

 which the Salmonidffi were not included. He remarked, "From this table it appears that the 

 size of the eggs is nearly the same in great and small fishes of the same species, at the same time 

 of the year." And these observations may be found, with but little variation, in the -writings of 

 authors from that period up to recent years, as perhaps in no branch of biology are assertions 

 once made more dogmatically adhered to, and that without re-investigation, than in Ichthyology. 

 Passing on to the Zoological Record of 1864, p. 179, we find that Professor Malmgren, having 

 observed that certain Salmonoids in a lake in Finland were descendents of the common Salmon, 

 whose access to the sea had been cut off o-wing to an elevation of the land, mentioned as one of 

 the present differences that this fresh- water and dwarfed breed gave smaller ova than Salmo salar. 

 In this conclusion Dr. Giinther did not coincide, remarking that "the last character [or size of 

 the ova] will be considered very significant by all who may have a more extended knowledge of 



