Migration of Birds

I HAVE waited for some time to see if anyone would ask Prof. Newton or Mr. Tegetmeier, on what evidence the latter gentleman has been led to `` declare that knowledge of landmarks obtained by sight, and sight only, is the sense which directs these birds,'' viz., carrier-pigeons. (See NATURE, vol. x. p. 416.) As no one has asked this question, I am obliged to do so myself; but at the same time I should like to say that it is only because the subject is one of great importance that I think we should not here be, satisfied with an authoritative statement of opinion, without some indication of the kind and degree of evidence on which such opinion is based. Moreover, it seems to me particularly desirable, that if a man of Mr. Tegetmeier's immense experience in this matter has any conclusive reasons for his decision, the public should have the benefit of their recital; so that the vexed question as to the `` homing '' of pigeons may once for all be settled.