FISHES 189 



place, that either the smallest male or the largest female has 

 the best chance of finding a mate and leaving progeny. 

 Darwin gave the evidence he collected in support of the 

 conclusion that the males were more numerous than the 

 females, but in the flat fishes Fulton's researches have shown 

 that the females are much more numerous than the males, 

 and there is no reason to suppose that the males prefer or 

 select the largest females. It may be suggested that the 

 largest females leave most eggs, and that, therefore, there is a 

 tendency to increase in the size of the females, but this would 

 not explain why the females should be larger than the males, 

 for the males would inherit the large size of their mothers. 



The difference in the size of body in the sexes may very 

 possibly be connected with the difference in the size of the 

 generative organs; the milts in the Pleuronectidae are generally 

 small in comparison with the size of the body, while the 

 ovaries are very large. But at present I am unable to see 

 how, on Lamarckian principles, the difference could have been 

 produced, and the selection principle appears to fail equally 

 in this case. 



Other unisexual characters occur in the Pleuronectidse. 

 One of considerable interest exists in the Plaice. In this 

 species the scales are for the most part reduced and rudi- 

 mentary, scarcely projecting from the skin, and having no 

 spines on the posterior edges like the scales of the dab or the 

 sole. But in the males, when they attain to sexual maturity, 

 spinules develop in connection with the scales on certain 

 parts of the body. This spinulation occurs in all individuals, 

 with few exceptions, on the middle fin-rays of the dorsal and 

 ventral fins ; when developed to a higher degree it occurs on 

 the head and operculum also, or, in addition, on the upper 

 side of the body in the region of the interspinous bones, or 

 over the whole of the upper side, and to a less degree on the 

 lower side. The higher degrees of the character are not 



