THE SALMON, THE TROUT, AND THE SHAD. 751 



tions for more than a year, (from September, 1873, till October, 1874,) I 

 became convinced that all the above-mentioned differences between the 

 winter-salmon and the spawn-salmon disappear with the advancing season 

 of the year and the progressing sexual development. From September 

 till about May, the differences between the two are so striking that, 

 without knowing the further development of the winter-salmon, they 

 would forthwith be declared to be two different species. I am, there- 

 fore, not at all astonished that the spawn-salmon (Salmo liamatus) has 

 been distinguished as a separate species from the winter-salmon (Salmo 

 salar) when both were seen together, without knowing that the differences 

 between the two were only temporary. From May onwards, the whole ap- 

 pearance of the winter-salmon changes, and gradually approaches that of 

 the spawn-salmon. The spots become more numerous; besides the black 

 ones, red ones make their appearance; the silver- white sides assume a 

 dirty -white color, while the back changes from a slate blue to a dingy 

 gray; the jaw of the male becomes elongated, and the hook is formed 

 in the lower jaw; the cceca lose their fat ; the flesh becomes paler and 

 drier; the milt and the eggs become larger in proportion ; and the edges of 

 the urogenital papilla back of the anus swell and become more prominent. 

 It is interesting to watch the growth of the ovaries. The ovary of the 

 above-mentioned winter-salmon, caught near Wesel on the 22d Septem- 

 ber, weighed at that date 13 grams. 1 According to my observations 

 of last winter, the weight of the ovaries increases very little up to April. 

 The ovary of a winter-salmon, caught in April of this year, weighed 19 

 grams ; of one caught in May, 22 grams ; in June, 48 ; in July, 91 ; in 

 August, 211; and the ripe ovary of a fish ready for spawning, (in Novem- 

 ber,) 800 to 1,000 grams. 2 



Two questions arise here : (1) Why does the winter-salmon ascend 

 the Ehiue long before it is able to spawn ? and (2) How long does 

 it remain in the river ? 



The first question is difficult to answer. In such cases, resort is had 

 to an " obscure instinct." This would in this case be the desire for pro- 

 pagating, although this cannot as yet be realized. It is true that all 

 salmons require a longer or shorter sojourn in fresh water for develop- 

 ing their sexual organs. 3 It is possible that, in the winter salmon, a 

 sojourn in fresh water, even if it be only temporary, gives the first impe- 

 tus toward the formation of the sexual organs ; this is, in fact, highly 

 probable. While in the sea, the fish has fattened so much that, if it 

 continued to take plenty of food, the milt and eggs would not develop 

 at all — a physiological fact which has long since been observed in other 

 animals. This development becomes possible by the fish's abstaining 

 from food while in the Ehiue. 



1 1 gram = 15.434 grains troy. 



2 In these figures, it must, of course, be taken into consideration that the fish from 

 which the ovaries were taken were not absolutely equal in age, size, and weight ; on 

 an average, they weighed 9 kilograms, (1 kilogram =2.205 pounds avoirdupois.) 



3 See Siebold, op. pit., p. 208. 



