[29] BIOLOGY OF THE RHINE SALMON. 455 
whether the facts at my disposal—especially the numerous measurements 
—will throw any light on these questions. x 
For this purpose I divided the salmon caught between Basel and Law- 
Senburg, keeping the males separate from the*females, and also sepa- 
rating the fish of 1878 from those of 1879 into groups of 20 millimeters 
difference, accepting as a constant their length (counting this with the 
males from the nostril, and with the females from the front part of the 
head, to the root of the tail), and from these groups constructed curves, 
the abscissas of which corresponded to the lengths of the fish, and the 
ordinates to the figures indicating the dates of occurrence of these lengths. 
The regularity of these curves* shows that they rest on a reliable basis, 
and at the same time proves the accuracy of the measurements. 
The first thing to strike us, with both sexes, is, that certain sizes are 
either entirely or almost lacking. If any further proof were required 
that not a single salmon goes through its entire development while in 
the Rhine, this fact would furnish it. From the line indicating 0, or 
from a slight elevation above this line, the curves showing the periods 
of migration rise like finely-shaped mountains with a maximum height 
and slopes on both sides. With the males, three elevations may be 
recognized in both years, resembling each other. The first gives the 
small salmon, the so-called St. Jacob’s salmon, weighing 1,500 to 3,000 
grams. As will be seen from the Dutch market reports, these are mostly 
late immigrants, which do not occur on the price-lists until July and 
August, and which, though in comparatively small numbers, reach us 
in September or October. The height of this curve, therefore, does not 
furnish an exact standard for estimating the numerical proportion of the 
immigration of these young fish. The second elevation contains such 
sizes as are found with us in September and October, with an average 
weight of 3,800 to 6,600; the third elevation shows the fish for the same 
months, but with an average weight of 6,600 to 13,000. If we had more 
data we would probably be able to construct a fourth elevation. Before 
proceeding any further we give the statistics in tabulated form: 
* These curves are not reproduced in the translation.—EDITOR. 
