1897. SPAWNING HABIT OF TELEOSTEAN FISHES. 389 



A. The stronger the drift (dependent upon the prevalent wind), 



B. The earUer in point of season the spawning takes place, 



C. The greater the bulk of the egg, — 



the further offshore must the spawn be deposited. 



It follows from this that in a given season of the year in any one 

 district, the larger eggs should be found (spawned) further out from 

 the shore, and that in the case of a species with a wide distribution in 

 time there should also be a wide distribution in place. In the limits 

 of this paper we can only add that these deductions are borne out to 

 a remarkable degree by the work which has been already done upon 

 pelagic eggs.' It is, however, interesting to note that by far the 

 largest British pelagic egg, that of the halibut, has not yet been found 

 in British (North Sea) waters, possibly because not sought for far 

 enough out to sea. 



When we consider the foregoing, there is little room for wonder 

 that many of the pelagic-spawning fish find it necessary to spawn 

 their eggs by millions, though it is probable that a further study of the 

 spawning-districts will supply definite reasons for the specific varia- 

 tion in fecundity. It is evident that, for the successful development 

 of the young fish, a concatenation of favourable circumstances is 

 necessary, which depends in the main upon such essentially fickle 

 phenomena as wind and temperature. Let the wind blow shorewards 

 with abnormal strength and duration, and untold millions of unhatched 

 cod may perish, or let the temperature for a few weeks during the 

 summer months be abnormally low, and the same fate may overtake 

 hosts of embryonic gurnards. Under such conditions it is only by 

 the selection of suitable spawning-sites, a prolongation of the spawning- 

 time (on the principle of not putting all the eggs in one basket), and 

 other devices, that the pelagic-spawning fishes have held their own. 



One might be inclined to inquire, Why do not all these fishes 

 spawn at the same most suitable time and have the same-sized eggs ? 

 The answer to this question brings out yet another avenue of destruc- 

 tion for pelagic eggs. Fertilisation of these eggs takes place in a 

 promiscuous manner, the sperms being freely shed in the water, and 

 diffusing themselves in a very rapid manner in all directions. Under 

 this system an enormous number of sperms and of eggs must perish ; 

 for though it is a rare thing to meet with unfertilised eggs in the 

 surface-water, yet it must be recollected that, if they do not meet with 

 a sperm, they soon sink to the bottom. It is conceivable, in the case 

 of such gadoids as the cod, which congregate together in " vast heaps," 

 that the mid-water in the whole district simply teems with the sexual 

 elements, and this loss from want of fertilisation is minimised ; but 

 in the case of the dab, a diffuse spawner, with no known pairing 

 instinct, there must be enormous losses. But from the very cosmo- 

 politan and ubiquitous character of these sperms there arises another 

 danger — namely, that of cross-fertilisation. Three or four closely- 

 1 See A.T.M. Rep. Fish. Board Scotland, xi.,/>. 250; 1S93. 



