384 NATURAL SCIENCE. June, 



reasons for maintaining that the pelagic-spawning fishes retain this 

 habit as a survival of a primitive condition, and that this habit is 

 therefore of phyletic significance. 



The enormous fecundity of these fishes has not up till now been 

 sufficiently emphasised nor its significance pointed out. Taken as a 

 measure of the amount of mortality amongst the young stages, it 

 points to the fact that this pelagic habit involves a subjection of the 

 young stages to powerful destructive agencies. Prof. G. O. Sars, in 

 his work upon the development of the cod/ recognised this fact, and 

 more recently a few observers have given expression to the same 

 ideas ; but it is not uncommon to find writers speaking of the great 

 advantages derived by pelagic eggs in that they are removed from the 

 danger of ravenous littoral enemies and even of the trawl. These 

 dangers are brought vividly home to the reader by graphic accounts 

 of countless shoals of haddock following in the wake of spawning 

 herring and feeding on the newly-shed spawn. Whilst granting the 

 truth of these statements, we must recall the fact that the few 

 thousand eggs of each female herring suffice to ensure the preservation 

 of the species, whilst it requires as many millions to perform the same 

 function in some of the gadoids. Some have attempted to explain 

 these facts by an appeal to the appetites of sundry copepods and 

 other crustaceans, to account for a great loss of pelagic eggs ; but 

 there seems to be no doubt that these eggs, by their very environ- 

 ment, are subjected to the vicissitudes of the physical world,^ the 

 destructive powers of which are not limited by the capacity of a 

 stomach, and which cannot be guarded against by translucency, 

 activity, or defensive armour. In changing their spawning-habit 

 from pelagic to demersal, some of the teleostean fishes have removed 

 their eggs and young stages from the action of every intermittent 

 change of wind, tide, and temperature to, in many cases, the direct 

 supervision of the parent. This change has been so successful that, 

 in spite of many enemies hunting the littoral region, the demersal- 

 spawning fishes can hold their own with far less tax upon the organic 

 energies of. the parent ; in other words, they do not require nearly so 

 high a fecundity. 



We may now enquire into the conditions of pelagic habitat, and 

 their effects upon the life-histories of the food-fishes. For this purpose 

 the eggs and early larval stages may be regarded as passive objects 

 so far as the determination of their own destiny is concerned. Some 

 modification of this statement may result from experiments now in 

 progress : the egg, a living object, may react to certain changes of 

 environment in a way which will have to be taken into account, and 



^ Report to Norwegian Home Department, 1864. 



2 C/. C. G. Petersen. 'It is my conviction, however, that the physical con- 

 ditions here play an exceedingly important part, and this is particularly conspicuous 

 if we try to imagine how all the larval fish which have come out of the eggs are to 

 reach the shore.' Report Danish Biol. Stat. 1S93, p. 15. 



