220 Mr. A. Newton on the Irruption of 



healthiest individuals will live to propagate their kind. It is 

 almost impossible that there can be enough Falcons to mate- 

 rially thin the ranks of, and keep down the numbers of, a bird 

 so swift and enduring in its flight as we know Syrrhaptes is. 

 The time necessary for incubation and the growth of the young 

 we also know, from Radde's observations, to be short in com- 

 parison with what it is in most ground-breeding birds. Syr- 

 rhaptes is therefore exempt from much risk which attends them. 

 Again, regard those acuminated primaries, those filiform tail- 

 feathers, those syndactylous feet, such as exist in no other 

 bird. Do not they indicate a highly specialized organization ? 

 Grant that the Sand-Grouse are, as a family, of inferior develop- 

 ment. Does not Syrrhaptes show, to borrow an expression 

 from that pregnant paper of Mr. Parker's (P. Z. S. 1863, 

 p. 258), " the culmination of the Pterocline type of structure" ? 

 Surely even those who refuse credit to the asserted validity of 

 " natural selection " when urged to its utmost limits, must admit 

 that this bird is probably the conquering hero of a long " strug- 

 gle for existence." Under this conjecture it may be literally 

 " seeking pastures new." It may have been striving to extend 

 its range in all directions ; if so, assuredly it will have found the 

 direction of least resistance. Northwards climatic causes would 

 probably hinder its expansion ; eastwards the country is already 

 stocked by its own race nearly as far as the Pacific ; southwards it 

 would trench on the district occupied by its big brother, *S^. tibe- 

 tanus; westwards therefore it must turn. It got its foot in 

 Europe as long ago as 1853, it may be longer ; we must allow 

 for the imperfection of our record. In 1859 it comes again, 

 the stress being now, with time, severer : possibly more birds 

 start, and the birds that start reach a greater distance. In 

 1863, from the same increasing pressure from within, still more 

 come, and come still further. If this notion be correct, unless 

 some physical change occurs in the Tartar steppes, which may 

 have the efi'ect of relieving the pressure, another outpouring may 

 be safely predicted, and probably the already thrice-found 

 channel will be again used by the emigrating population. Let 

 us look then to the naturalists of llussia, on whom the mantle 

 of Pallas so worthily rests, to enlighten us still further as to 



