[27] BIOLOGY OF THE RHINE SALMON. ADd3 
no means one. of barrenness, but one of retarded formation of normal 
elements. These fish are, as a rule, called winter salmon, and fetch 
prices like these; but they must by no means be confounded with the 
genuine winter salmon described above, which do not spawn till Novem- 
ber and December of the following year. 
The observations which I made relative to these late-comers are, in 
my opinion, a certain proof that for the male fish the short migration- 
period from the sea to Basel does not suffice to complete the entire sex- 
ual development up to the point of maturity, much as the rate at 
which this development goes on may vary between individual fish. The 
probability, therefore, becomes still greater than would appear from 
what has been said above, that the entire spawning generation of one 
year consists of fish which have staid in the Rhine several months 
longer than the shortest period occupied by the migration from the sea. 
Neither during the spawning season nor later have I seen female 
fish whose general appearance stamped them as fresh immigrants ; it 
is a matter of doubt with me whether the very rare, fall-ripe female 
fish which occurred in January 1879 and (in 1880) even as late as Feb- 
ruary 20 belong to this category. I had my suspicions regarding a 
very lean fish, of the middle of November, 1879, which had a clear 
skin, and an ovarium only weighing 16.5 per cent. of the weight of the 
body, and containing comparatively small eggs; all this, however, 
might have been caused by the unusually small quantity of flesh. 
The different links of the long series of internal and external changes, 
by which the spring salmon is transformed into the spawning salmon, 
run, as a general rule, parallel, but not with mathematical accuracy. 
The gristle of the nose and chin begins to grow before there is any sign of 
development in the testicles; and before the testicles have reached one- 
eighth of their mature weight the skin oiten shows very distinctred spots. 
It would also frequently lead to mistakes if one were to determine— 
say in August or September—the stage of development of the sexual 
glands by the degree of development to which the hook formation has 
attained. On the one hand we see the influence of the different seasons 
of migration, and on the other hand we see the effort (notwithstanding 
this difference) to finish the sexual development for the same time of 
spawning. In short, the development of the sexual organs is not the 
direct cause of external influences, but is only indirectly connected with 
them. : 
Finally, I have to make brief mention of an internal organ which 
exhibits some very curious phenomena. The spleen, which is now gen- 
erally considered as a gland forming blood, appears in the winter sal- 
mon as a tough, brown, insignificant organ, weighing about yooe to 
soso Of the weight of the body. In May a swelling is observed to 
commence in the female fish, in the shape of dark-red raised knots, 
which increase ix size and number, and combine, till, about the end of 
June or sometime in July, the organ has reached 15 to 20 times of the 
