ON THE ECONOMY OF EEES. 357 



following circumstances lead me to believe that sex is not given to the 

 eggs of birds, or to the spawn of fishes or insects, at any very early period 

 of their growth. 



I selected early in winter four female birds of the common duck, which 

 I kept apart from any male bird of that or any kindred species, till the 

 period of their laying eggs approached. One was then killed, and the 

 largest of its eggs was found to be three lines in diameter. A musk drake 

 (Anas moschata) was then put into company with the three remaining 

 ducks ; and from these I obtained a numerous offspring, six out of seven 

 of which proved to be males, as the result of similar previous experiments 

 (but in which the male of another species had been introduced at a period 

 when the growth of the eggs was less advanced,) had led me to expect. 

 I repeated the experiment often, and always with nearly the same result, 

 a large majority of male birds being uniformly produced ; and hence I 

 conclude that the eggs of birds in early periods of their growth are 

 without sex. 



I have never possessed means of obtaining mule fishes ; but one kind 

 of fish, which I think is obviously a mule, is found in many rivers where 

 the common river- trout abounds, and where a solitary salmon is sometimes 

 seen. These formerly existed, in some seasons, in considerable numbers, 

 in the river which passes near my residence ; but since salmon have 

 become scarce, they have wholly disappeared. I had formerly opportu- 

 nities of examining a large number of them, without having ever found a 

 single female. I have subsequently found them in large numbers in small 

 mountain rivulets in Wales, below, but never above, the lowest cataract. 

 They are readily distinguished from the young salmon, by their form 

 being intermediate between that of a trout and of a salmon ; by their 

 being all, or nearly all, males ; and by their remaining through the sum- 

 mer and autumn in the rivers, long after the young salmon have descended 

 to the sea : they leave the fresh water with the first winter floods, and I 

 believe are not known ever to return. In the north of England they are 

 distinguished by the name of wrackriders, and by that of samlets in some 

 other parts. If these be mules, as I do not entertain any doubt that 

 they are, the spawn of fishes must be without sex when it is deposited by 

 the female; and I am much disposed to entertain the same opinion 

 respecting the spawn (for it is more properly spawn than eggs) of bees. 



I have frequently witnessed some somewhat analogous circumstances in 

 the vegetable world, respecting the sexes of the blossoms of plants ; and 

 I can at any time succeed in causing several kinds of monoecious plants 



