68 Recent Literature. I Jan 



tion seems little short of a fascination with some naturalists, and promi- 

 nent amongst these, we deeply regret to say, must be included such a 

 veteran and accomplished observer as Herr Gfitke, whose anti-Darwinian 

 and anti-evolutionistic views may very probably be responsible for the 

 position which he has taken tip with regard to this portion especially [of 

 how birds find their way] of the phenomenon of avine season-flight." 

 Consequently it is not surprising to find many pages devoted to an 

 exposure of the fallacies contained in ' Heligoland,' and an attempt to 

 counteract the undesirable effect of copying as " ex cathedra " these " wild 

 speculations," and "startling estimates of the speed at which birds fly," 

 into many popular works on the subject of migration. This lament is 

 doubtless widely shared by thoughtful students of the subject. 



Mr. Dixon here offers us, however, a new theory of the origin 

 of migration in birds, all previous theories, in his opinion, proving 

 untenable. The new hypothesis is founded on what he claims " to be a 

 hitherto undiscovered law governing the geographical distribution of 

 ^species," which he terms " the Law of Dispersal." This law is based on 

 the following assumptions: (i) That there was formerly a vast extent of 

 intertropical land, stretching continuously around the globe, in which 

 life originated and from which life has spread in the direction of the 

 poles. A former extensive antarctic continent, which some writers believe 

 ■once existed, he considers as having no bearing on the question ; from 

 his point of view, the form.er great extension of land must have been 

 equatorial. The very general belief in the comparative permanence 

 ■of the principal oceans and land masses, held so firmly by nearly all 

 geologists of high standing, he thinks is without foundation, and that 

 this erroneous view is responsible for the mistaken opinions now so gen- 

 erally held on the subject of the origin and cause of migration. (2) He 

 affirms that the Glacial Epoch could not have been the inducing cause of 

 migration in the northern hemisphere; the belief that species began "to 

 reti-eat or emigrate beyond the influence of the adverse conditions of 

 existence, as the climate changed and became more severe " is absolutely 

 opposed, he says, by all the facts ; in other woi'ds, as he repeatedly 

 afliirms, an emigration southward to escape the adverse conditions of the 

 advancing ice' age, is a myth. There was no movement southward of 

 any species ; they were simply exterminated ; "the only forms that sur- 

 vived this several times repeated glacial invasion were those whose 

 pre-glacial breeding range extended beyond its influence." The current 

 opinion "that species evacuated their northern homes as the glacial 

 periods came on, and returned to them, more or less modified, as the 

 climate ameliorated," is, in his opinion, "an entirely erroneous inter- 

 pretation of facts." (3) Migration, he claims, is the corollary of emigra- 

 tion ; both are due to an effort to increase the breeding range of the 

 species, and the lines of migration are always along the old routes of the 

 gradual range extension of the species. (4) Spring migration is due 



