180 
ZOOLOGICAL LITERATURE. 
species retained the purity of their characters^ but some of them, 
becoming exposed to a change of external conditions, underwent 
a corresponding change in a part of the original characters. 
Now, as this may have happened to only a certain number of the 
individuals of a species, the altered form of the present day is 
not entitled to the rank of species, but is to be considered a 
variety. Although we doubt very much whether zoologists 
would ever make practical use, for the distinction of species, of 
this doctrine even if it should prove true, we do not find it sup- 
ported by the facts bearing upon this question. 
1. According to the excellent researches of Professor Loven, 
quoted above (p. 137), a certain number of arctic marine animals 
still survive in great depths of the Scandinavian lakes, from the 
period at which those lakes were separated fr’om the Glacial 
Ocean ; they have not changed their characters^ but are smaller 
in size. 
2. Profiting by this discovery. Hr. Malmgren finds that a 
number of certain marine fishes still inhabit the gulf of Bothnia, 
being the remnants of the arctic fauna of the period when the 
Baltic was a gulf of the Glacial Ocean. They agree, in spite of 
the change of the water, with their brethren in the White Sea in 
every character, except in size. 
3. Therefore these two facts directly contradict the hypothesis 
that two Salmonoids inhabiting those lakes are the modified 
descendants of marine fishes, the true types of which are con- 
tinued to the present day in those forms which, propagating 
their species under the original conditions, have remained un- 
altered. 
Yet it may be said that some species changed their original 
characters, whilst others preserved them under all circumstances. 
To this we have no other method of replying than of entering 
into an examination of the characters which must have been 
affected in those lacustrine forms. 
We have not seen specimens of the Trutta relicta^* from 
Lake Ladoga, but they are stated to be identical with those of 
Lake Wener, of which we have received splendid examples 
through Mr. Wheelwright ; and although we cannot place full 
confidence, as regards specific identification or distinction, in 
Messrs. Widegren and Malmgren, who are so apt to confound 
species, our Wener specimens answer our purpose quite as well 
as those from Lake Ladoga would do. Now the one considered 
to be the descendant of the Salmon differs from that species, 
first, in having much smaller scales, the large-sized scales of the 
tail being one of the principal and most constant characters of 
the Salmon ; secondly, in the number of pyloric appendages; and 
thirdly — as Hr. Malmgren observes — in the size of the ova. 
The last character will be considered very significant by all 
who may have a more extensive knowledge of fishes, as the size 
