[33] BIOLOGY OF THE RHINE SALMON. 459 
do not consider it impossible that among the later immigrants of 1879 
there are many male fish which have still gone through the spawning 
period of 1878. This supposition would be the easiest explanation of 
the fact that—the length being equal—the winter and spring salmon 
are so much fatter and heavier than those among the August and Sep- 
tember male fish (near Basel) which show indications of recent immi- 
gration in their color and nose, because the former have had more time 
to fatten in the sea. The same proportion would also apply to early 
and late salmon if the recent immigration of male fish from the spawn- 
ing period 1878 would be placed in the year 1880. Supposing that the 
majority of the male salmon returns every year, there results a lowest 
possible minimum age for a male salmon begotten on the Ist December, 
874, and hatched on the 1st February, 1875, which participated in all 
‘three migrations, viz: 
First migration (as young salmon) to the sea, spring of 
Meso) 3 Sg 2s |e ae a SAP ene About 1 year. 
First spawning season (as St. Jacob’s salmon), near 
Basel, partly in December, 1877, and partly in 1878. 23 to 33 years. 
Second spawning season (as salmon proper), weighing 
3$ to 64 kilograms, December, 1878, and 1879 ...... 33 to 43 years. 
Third spawning season (as salmon proper), weighing 
64 to 13 kilograms, December, 1879, and 1880 ..-.-- 43 to 52 years. | 
I must, however, consider it just as probable that every interval be- 
tween the three last stages is one year longer; for I must confess that 
I cannot willingly accustom myself to think that so fine a fish as the 
salmon should be destined to starve throughout the greater portion of 
its adult stage, antl should only eat with feverish voracity during short 
intervals between the starving periods, and yet grow during such peri- 
ods at an enormous rate. 
I think, moreover, that the influence of the feeding-process is rather 
overestimated, by supposing that, in 14 years, the small migrating sal- 
mon, weighing only 20 to 25 grams and measuring 7 to 9 centimeters,* 
should be transformed into the St. Jacob’s aot which returns in 
June or July, and is seven times as long and 100 to 150 times as heavy, 
whilst the two-year old salmon of our waters which has remained with us, 
and which I occasionally observed, weighs about 80 to 100 grams. We 
would, therefore, certainly have to allow 2} years for development from 
the a migrating salmon to the St. Saco s salmon, and for the large 
St. Jacob’s salmon probably one year more. 
But why should we trouble ourselves with suppositions regarding a 
size which can be accurately determined according to our methods? 
*AsI did not have an opportunity to personally examine any specimens, I make 
use of an estimate by Mr. Glaser, which may have to be corrected. 
+A very successful experiment was made to produce impregnation w ith the semen 
of such a salmon weighing about 100 grams. Ihave never seen mature females of 
this kind. 
