P39] BIOLOGY OF THE RHINE SALMON. 465 
The winter salmon are, in my opinion, therefore, fish which have been 
én the sea for alonger period of time, compared with the majority of their 
future companions in spawning, either— 
(1.) By having skipped the entire spawning period by a period of 
more than one year; or, 
(2.) By letting one more years intervene between two spawning peri- 
ods. Possibly both cases occur. 
The fish have thereby become longer than the majority of their future 
companions in spawning; they consequently belong to the right half of 
the third curve (showing size), but they have also become fatter, and 
therefore immigrate earlier, in order to reach their normal spawning 
condition. The gain in time which they have made is divided into an 
increasing and a decreasing phase, whereby they again reach the level 
of the rest.* 
There may also be smaller fish, which go through the same course, 
because during the normal period they had an opportunity to fatten to 
an extraordinary degree. It is also possible that some fish which, as to 
age, correspond to the winter salmon,t on account of not having ready 
access to suitable food, join the later immigrants. 
In reviewing this whole question one should not be led astray by dif- 
ferencs of shape, which may occasion great differences of weight in fish 
whose length is the same. I would therefore recommend not only an 
analysis of the flesh of the body, but more especially the proportion of 
the muscles of the pectoral fins to the weight of the body, as a standard 
by which to measure the amount of reserve substance contained in the 
body. 
It will also appear from the above remarks that it would be a mistake 
to determine the emaciation by two series of data showing the weights 
of fish at any two periods differing about two months. The influence 
of great masses of salmon coming in July would disarrange the curve 
still more, if the new immigrants were not somewhat leaner to begin 
with. We therefore (possibly) owe the plausible result, in part at least, 
to the fact that various mistakes neutralize each other. Not till the 
middle or end of July, when from other causes I must consider the 
immigration of females into our waters as almost finished, can I pay 
closer attention to the figures indicating emaciation; in my opinion it 
is only tfrom.that time that the actual change of substance (Stoffwechsel) 
commences. 
I have finally to direct attention to a sort of counterpart of the fat 
winter salmon. In reviewing the six groups (or divisions) of female 
salmon, each containing fish of equal length, considerable variations 
* Some exceptionally lean spring salmon had fallen off very much owing to an in- 
vasion of leeches; they had gatherings in various parts of the body, and the rays of 
the fins had begun to fester. Not every lean spring salmon can, therefore, be adduced 
as proof against the truth of my view. 
t Only those muscles which form the bones of the extremities extend to the basis of 
the rays of the fins. 
S. Mis. 29-———30 
