AnTHUR.— n the Brown Trout introduced into Otago. 505 
also frequently seen the upper lobe larger than the under one. The least 
depth of the tail is pretty constant, being from a tenth to a twelfth of the 
total length of the trout, or about that ratio. 
But, as the size of the fins is thought by naturalists to have a direct 
relation to the depth of water and nature of the bottom, it may be well to 
see what evidence my specimens can give on that point. Dr. Giinther 
says :—*“* Those individuals which live in rapid streams, being in almost 
constant motion, and wearing off the delicate extremities of the fins, have 
the fin-rays comparatively shorter and stouter, and the fins of a more 
. rounded form, particularly at the corners, than individuals inhabiting ponds 
or lakes.” * The number of trout I have measured with particular reference 
to this question is not, in my opinion, sufficient to test the case fairly in 
Otago waters. Out of 13 rivers, I have had 19 males and 6 females under 
measurement, also 2 males from Lake Wakatipu; these are all. I have 
classified them, however, distinguishing fish from rapid and rocky streams, 
as separated from those frequenting larger and stiller water; and I find 
that the evidence is very puzzling and contradictory, so that different 
theories might easily be based on particular cases. I have therefore pre- 
pared a large table, showing the ratio which each fin bears to the total 
length of the fish—measuring the base of the single or median fins and the 
longest ray of the double fins, as representing the lengths. The result on 
the whole, and taking it for what it may be worth, is corroborative of the 
above quotation from Giinther. Three of the fins, viz., the dorsal, pectoral, 
and ventral, I find shorter in the rough, quick-running rivers, than in the 
stiller, heavier streams, or in the lake; but the anal is doubtful. While, 
therefore, my experiments on this point are not so complete as could be 
desired, they have brought out other facts curious and interesting, and 
which are not so open to dubiety. Thus I find the females have all smaller 
fins than the males, excepting the anal, which is larger. Then, among the 
females, the range of difference or variation in the size of fins is very great 
as between different individuals, and also between the different fins of the 
body themselves. But, among the males, the range is not nearly so great ; 
neither is there the great difference of size between the body fins them- 
selves. These latter facts will appear more clearly from this short 
table :— 2 
Range in ratio of fins to total length of trout. 
D p v 
Females aa; 1:38 Lù 1:93 e 2:10 x 4-86 
Males .. 0:93 oe 0-91 .. 1:44 .. 0:94 
* Study of Fishes, p. 634. 3 
