38 Mr. Robert Collett on 



All these transition-forms (possibly witli but one solitary 

 exception) were males ; also the last-mentioned variety. 



The question as to when and in what condition these 

 specimens of L. excubitor, either with no or with an imper- 

 fectly developed basal spot on the secondaries^ are found to 

 occur, can hardly at present be satisfactorily settled. 



First of all, it is evident that the presence or absence of 

 the basal spot on the secondaries cannot be dependent on 

 age, since both single-spotted and double-spotted individuals 

 belonging to the same brood occur even in the nesting- 

 plumage. 



Furthermore, should the varying colour of the secondaries 

 arise from a gradual change, and the imperfectly developed 

 basal spot in the course of the winter and spring become a 

 perfect one (as with the primaries of Plectrophanes nivalis, 

 which pass, without moulting, from brownish grey to white), 

 a change in this respect would necessarily take place with 

 such individuals also as exhibit a very small or no basal spot 

 whatever on the secondaries, and not in transition-specimens 

 alone. 



Thirdly, sex exerts no decided influence, although single- 

 spotted individuals are more frequently found to be females 

 than males. 



Finally, as regards the latitude, it is generally admitted 

 that the single-spotted form (comprising also less typical or 

 transition individuals) belongs to the northern or north- 

 eastern tracts of the Palsearctic Region, whereas the typical 

 L. excubitor inhabits Western and Central Europe. Mean- 

 while we must bear in mind that every year, now that 

 attention has been drawn to the subject, more or less typical 

 specimens of the single-spotted form {L. majoi', Cab.) are 

 shown to occur regularly or commonly in most tracts along 

 with the normal L. excubitor, extending to Austria and 

 Hungary; while, as stated above, the true L. excubitor has 

 also been found to inhabit and breed in the Arctic regions 

 (Finmark) . Other examples are recorded from Archangel 

 (Meves), from the Ob (Finsch) ; and their number will 

 assuredly increase every year. 



