376 THE ZOOLOGIST, 



which I received specimens of two, Hirundo puella and H. sene- 

 galensis. One, described as white underneath, is probably 

 H. cethiopica ; and the fourth, very small and quite black, must 

 be a Psalidoprocne. All these remained through spring and 

 summer. The northward movement of all the others must be 

 through some impulse not yet ascertained. In many other in- 

 stances observation has shown that the impulse of movement is 

 not dependent on the weather at the moment. This is especially 

 the case with sea birds. Professor Newton observes they can be 

 trusted as the almanack itself. Foul weather or fair, heat or cold, 

 the Puffins, Fratercula arctica, repair to some of their stations 

 punctually on a given day, as if their movements were regulated 

 by clockwork. In like manner, whether the summer be cold or 

 hot, the Swifts leave their summer home in England about the first 

 week in August, only occasional stragglers ever being seen after that 

 date. So in three different years in Syria I noticed the appear- 

 ance of the Common Swift (Cypselus apus) in myriads on one day 

 in the nrst week in April. In the case of almost all the land 

 birds, it has been ascertained by repeated observations that the 

 male birds arrive some days before the hens. I do not think it 

 is proved that they start earlier; but, being generally stronger 

 than the females, it is very natural that they should outstrip their 

 weaker mates. I think, too, that there is evidence that those 

 species which have the most extended southerly, have also the 

 most extended northerly range. The same may hold ;good of 

 individuals of the same species, and may be accounted for by, or 

 account for, the fact that, e.g., the inividuals of the Wheatear or 

 of the Willow Wren which penetrate furthest north have longer 

 and stronger wings than those individuals which terminate their 

 journey in more southern latitudes. The length of wing of two 

 specimens of Saxicola oenanthe in my collection, from Greenland 

 and Labrador, exceeds by 0*6 the length of British and Syrian 

 specimens, and the next longest, exceeding them by 0*5 inch, is 

 from the Gambia. So the sedentary Phylloscopus trochilus of 

 the Canaries has a perceptibly shorter wing than European spe- 

 cimens. 



To say that migration is performed by instinct is no explana- 

 tion of the marvellous faculty, — it is an evasion of the difficulty. 

 Professor Mobius holds that birds crossing the ocean may be 

 guided by observing the rolling of the waves ; but this will not 



