i88i.] 
39 
Analyses of Books . 
of mosquitoes will rise between you and the sight,” We wonder 
how those writers who seek to represent the mosquito as a sani- 
tary agent, without whose aid “ no animal higher than a reptile 
could have existed,”* will explain its presence in regions where 
malaria is altogether out of the question ? But there is a further 
difficulty; how has such a taste for blood become developed 
among a race of beings not one in a million of whom ever tastes 
it, or even comes within scent of man or other mammal ? How 
is it that the birds, especially when unfledged, escape their 
attacks ? 
The author mentions with surprise that he saw three speci- 
mens of the common gull ( Larus canus ) perched upon a tall tree, 
a phenomenon which may be witnessed at home. 
Perhaps the most interesting chapter of the work is one 
written at Heligoland, and treating of the migration of birds. 
Mr. Seebohm considers that migration is comparatively of recent 
date. “ It is not confined to any one geographical region, nor 
to any one family of birds, nor can he assume that it will be pre- 
sent or absent in every species of the same genus.” He pro- 
poses the law that every bird breeds in the coldest, country of its 
migrations. The stories of birds breeding a second time in their 
winter residence have, he holds, “ the same scientific value as 
the stories of swallows having been found hybernating in caves 
and hollow trees.” He reminds us that some species, such as 
the robin, the blackbird and the song-thrush, are stationary in 
England, but migratory in Germany. He suggests that these 
birds have only recently ceased to migrate in England, so that 
should our climate remain long enough favourable to their 
winter abode they will develope into local races with rounder and 
shorter wings than their continental kindrtd. He considers that 
birds were originally resident in the district where they now 
breed, and that the cause of their wanderings is want of food, 
not want of heat. But he remarks that it is supposed that many 
birds leave their winter quarters in southern climates because 
the heat dries up everything, and lessens the production of inseCt 
life.” Now in the valleys of Asia Minor, in the gorges of Par- 
nassus, &c., he found inseCts in profusion in May and June. 
Why then do inseCt-eating birds leave those regions in the 
summer? Not, on his own showing, from lack of food. 
Mr. Seebohm doubts the correction between the routes fol- 
lowed by migratory birds and the position of submerged lands. 
He holds that the desire to migrate is a hereditary impulse to 
which the descendants of migratory birds are subjeCt in spring 
and autumn, and which has in the lapse of ages acquired a force 
almost as irresistible as the instinCt to breed in spring. “ The 
direction in which to migrate appears to be absolutely unknown 
to the young birds in their first autumn, and has to be learned by 
Journal of Science, 1875, p. 225. 
