78 SECTIONAL ADDRESSES. 
rounded subterminal mouth of several kinds which always feed at the 
“bottom. I confess that I do not understand why the scales are much 
smaller and more numerous in the char of some lakes than in those of 
others, but I suspect that these differences in scaling are the expression 
of physiological differences and are the result of differences in the environ- 
ment or in the activities of the fish. 
The genus Salmo comprises about ten species from the North Atlantic 
and the North Pacific, and I have shown that the salmon and trout of 
the Atlantic form one natural group and those of the Pacific another. 
Our own salmon and trout are two closely related species ; both of them 
range in the sea from Iceland and northern Norway to the Bay of Biscay, 
both enter rivers to breed, and in both the young fish, known as parr, 
remain in fresh water until they are about two years old and six inches 
long, and then go to the sea. From Mr. F. G. Richmond, a well-known 
pisciculturist, I have the information that although at certain seasons the 
parr of both salmon and trout may eat the same kind of food—for example, 
both take flies at the surface—yet on the whole their food and feeding 
habits appear to be different. Salmon parr seek their food, such as insect 
-larve, small molluscs and crustaceans, on the bottom, whereas young 
trout tend to keep in mid-water and to subsist more on water-borne food ; 
thus the salmon parr may be hunting for food in a stretch of shallow 
rapid water, while the young trout wait for it in the quieter water just 
below. When they are about six inches long the parr of both species 
become silvery and are termed smolts; the trout smolts go to the sea in 
a leisurely manner, hanging about the estuaries, and the older fish frequent 
the coastal waters; but the salmon smolts make straight for the open 
sea and there grow much faster than the trout, attaining a weight of 
several pounds in a year. 
I have gone into these details because I think it is important to estab- 
lish that two closely related species in the same area have different habits, 
and to a large extent avoid competing with each other. 
The morphological differences between salmon and trout are slight. 
The salmon, more active and a stronger swimmer, is more regularly fusi- 
form in shape and has a more slender tail and a more spreading and more 
deeply emarginate caudal fin, differences of the same kind but not of the 
same extent as between a perch and a mackerel. Therows of scales between 
the adipose fin and the lateral line are usually fewer (10 to 13) in the salmon 
than in the trout (12 to 16); but this may be directly related to the fact 
that the tail is more slender. On an average the salmon has one ray more 
in the dorsal fin than the trout, and I am tempted to regard this as a step 
towards that increased number and concentration of the dorsal rays 
which is so characteristic of swift-swimming pelagic fishes. The last 
difference between the two species—the smaller mouth of the salmon— 
may be related to the food and feeding habits of the parr. In structure as 
in habits the salmon is more specialised than the trout, and may have 
evolved from it. The salmon is found on the Atlantic coast of North 
America, where there are no trout; but I think this is because its habit 
of going farther out to sea has given it a greater opportunity of extending 
itsrange. There can be little doubt that the differentiation of these species 
has been not geographical but habitudinal, comparable to the differentia- 
tion of the coastal and open-sea herrings. , 
