24 On the present state of Zoology. 
attempted to establish no less than seven species of Loxia, or true 
Crossbill, as natives of Germany.* The same observer has made three 
species out of Columba lima ; three out of Emberiza nivalis ; two 
out of Anas glacialis ; two out of Larus marinus ; the same out of 
two other species in that genus ; two out of Procellaria glacialis ; 
besides many more which it would be tedious to enumerate. When we 
find opinions of this nature entertained, and we imagine it would not 
be difficult to adduce similar examples in the other departments of 
Zoology, can we believe that due attention has been paid to those va- 
riations of character, which we see constantly arising from local or 
accidental circumstances in other species, and which in these last we 
can indubitably trace back to such causes only ? With respect to birds 
in particular, we cannot be too cautious how we place reliance upon 
mere variations of plumage ; over which we know so great an influ- 
ence to be exerted by age, sex, season, and have ground to suspect, 
in certain instances, also by climate. We know, moreover, that some 
of the changes arising from these causes are themselves liable to ir- 
regularity from any accidental circumstances affecting particular in- 
dividuals. This is especially the case with those due to differences 
of age, as has been proved by rearing birds in confinement. It has 
been observed that, under such circumstances, an interruption often 
takes place for a longer or shorter period, possibly in some few in- 
stances an entire suspension, of laws, which would otherwise operate 
uniformly for each species respectively. Thus it is mentioned by F. 
Cuvier,f that Gulls, which in a state of liberty would naturally ma- 
ture their plumage at the end of the second or third year, have been 
known in captivity to require one or two years more for that pur- 
pose. Analogous facts have been observed in our own country. With 
respect to the influence of climate in bringing about a permanent dif- 
ference of character in certain species, as compared with the same 
species found in other latitudes, it is a subject upon which little posi- 
tive information has been yet obtained. We may, however, fairly 
contend that the thing is possible, if not highly probable, till some 
direct arguments be adduced against it. Assuming, as a fact, that 
season and temperature cause periodic changes in the plumage of some 
species ; it seems highly probable, that any thing which occurs to 
disturb the regularity of the seasons or to affect their general charac- 
ter, may affect, in like manner, the regularity of such changes, or at 
least modify the extent to which they are carried. Now any parti- 
cular season departing from its usual character in this manner, may 
* Bull, des des Sci. Nat. 1828, torn. xiv. p. 259. 
f Ann. du Mus. torn. xi. p. 285. 
