28o A HISTORY OF FISHES 



are quite promiscuous. This is especially the case in those fishes 

 Hke the Herring (Clupea) and Cod [Gadus), which congregate 

 together in dense shoals at certain seasons for the purpose of 

 spawning. The actual reproductive act is, of course, essentially 

 similar to that of all the higher vertebrates, and consists in the 

 fusion of two kinds of gametes or "marrying cells," the eggs or 

 ova of the female and the spermatozoa or sperms of the male 

 (sometimes referred to as the milt). The difference Ues in the 

 manner in which this fusion, or fertiUsation, as it is called, 

 takes place. Whereas, in the mammal this occurs within the 

 body of the female as the result of conjugation between the 

 sexes, and the fertilised egg develops within a special chamber 

 in her body, in the generality of fishes the ova and sperms 

 are merely shed into the water, where fertilisation takes place. 

 Under such conditions it might reasonably be expected that 

 the proportion of eggs escaping fertilisation would be rather 

 high, especially where spawning takes place in the open sea. 

 This is not the case, however, and in the Plaice (Pleuronectes) , 

 each female of which extrudes as many as from 250,000 to 

 500,000 eggs in a single spawning season, unfertilised eggs are 

 very rarely found. 



The difficulty of observing the actual process of spawning in 

 certain fishes led to the advancement of some peculiar and 

 generally highly inaccurate theories as to the manner in which 

 they reproduced their kind by the older naturalists, and many 

 of the explanations given by classical authors make amusing 

 reading to-day. Oppian, for example, describes how fishes are 

 overcome by the "passion of love," and the bodies of the male 

 and female meet in the water and "exude mingled slime," 

 which when swallowed by the female produces conception. 

 The great Aristotle came little nearer to the truth. "In point 

 of fact," he wrote, " some are led by the want of actual observa- 

 tion to surmise that the female becomes impregnated by 

 swallowing the seminal fluid of the male. There can be no 

 doubt that this proceeding on the part of the female is often 

 witnessed; for at the rutting season the females follow the 

 males and perform this operation, and strike the males with 

 their mouths under the belly, and the males are thereby 

 induced to part with the sperm sooner and more plentifully. 

 And, further, at the spawning season the males go in pursuit 

 of the females, and as the female spawns, the males swallow 

 the eggs ; and the species is continued in existence by the spawn 

 that survives this process." Even Izaak Walton, writing in the 



