NATURAL HISTORY SOCIETY OF GLASGOW. 135 



be found in the absence of a proper supply of the usual food, 

 and a consequent constitutional change; a want of the usual 

 colouring principle, or from sickness, or wounds ; in such instances, 

 it would increase with age, and become hereditary, as it un- 

 doubtedly is. 



Since the above was written, I have heard of another covey of 

 these birds showing the same variety, with the horse-shoe white. 

 Mr Arthur Dundas told me that this winter he shot three of 

 these birds on Carronhall estate, near Falkirk, one of which was an 

 old bird. All, both old and young, had brown or buff chins and 

 throats, and white horse -shoes on the breasts, like specimen 

 No. 3. 



AVhen on the subject of variation in species, I may make a few 

 remarks upon this unusually dark form of our common sand 

 martin, which I believe has every bit as much right to be con- 

 sidered a good species as dozens of other constant varieties have. 

 This bird was shot by me on the Petchora River, in north-east 

 Russia, in 1875. All the sand martins observed by us either at 

 Archangel or eastward have this dark phase of plumage, and at 

 Archangel there are legions of them nesting in every suitable 

 situation. Now what is remarkable about these sand martins is, 

 that in them the reverse of the following general rule is 

 exemplified: ''Continental forms of birds are usually brighter 

 and lighter coloured than insular ones, and eastern European 

 forms are almost invariably lighter than their western representa- 

 tives." I may here instance one or two of many cases which 

 occur to me of the above rule, so as to put the case of the sand 

 martins of North Russia from a stronger point of view. 



Our English marsh tit, Parus ixdustris, when compared with 

 the more northern Norwegian form, Parus borealis, will be found 

 to be very much darker. When compared again with the Siberian 

 marsh tit, Parus kamschatkensis, which we found in the Pet- 

 chora, the difference becomes marked indeed, the latter being 

 very much lighter — mealier — than our bird. 



Parus cinctus — the Lap tit — of northern Scandinavia is darker 

 than Parus griscescens of Dresser from Siberia, while the form we 

 procured on the Petchora shows an intermediate phase. PraUncola 

 rubicola, our stonechat, has the rump spotted. The eastern 

 brighter form, PraUncola inclica, has the rump unspotted j we found 

 this also on the Petchora. 



