i 



Variatiom in the Animal Kingdom. 16 



which they had large numbers, and which, instead of having a 

 hard blue-black shell, possessed a thin yellowish brown shell, in 

 many cases beautifully banded. So far as I could ascertain, 

 these mussels were obtained from a very dirty and brackish 

 water locality ; whether that was the cause of their variation I 

 do not know, but the variety certainly occurred in sufficient 

 numbers to be honoured with a name, if not to form a species. 

 No doubt the external conditions had been changing, and in- 

 fluenced a pro rata adjustment of the internal condition, or 

 secretory organs, of the animal. I am inclined to think that 

 the geological character of a locaUty has some influence upon 

 the organisms living in that locahty. Of course this is un- 

 doubtedly true of land organisms, for the simple reason that an 

 animal keeps to where its food-plant is. But in regard to 

 marine organisms, this is different, at least to a very great 

 extent. If, however, we take a very common crustacean, Car- 

 cinus mmnas, which occurs on all parts of our coast near tide- 

 mark, irrespective of whether the locahty be clay, sand, lime- 

 stone, or granite, we find that there is a decided character of 

 colour and markings, according to the nature of the rocks of the 

 place from which the specimen is obtained ; the markings being 

 brilliant on those from granite areas, almost black and very 

 dull from clay or muddy shores, and tawny from yellow ones. 

 This, of course, is due to adaptation to surrounding conditions. 



Burrowing crustaceans possess no bright colours, and their 

 dull tints almost invariably correspond to the colour of the 

 material into which they burrow, thus showing complete corre- 

 spondence, and therefore life in, so far as this class is concerned, 

 its safest aspect. 



It seems probable that climate has a marked effect on colon- 

 zation, and perhaps markings too; certainly the proximity to 

 the sea has, for when visiting the Fame Islands I examined the 

 sand-dunes on the shore near Bamborough, where I found many 

 hundreds of the little banded snail. Helix nemoralis, of almost 

 every possible variety of colour and markings, many of them 

 very beautiful ; but the typical form of this species was positively 

 absent, there were none ; nor do I know of any inland loeahties 

 where the varieties I found occur. In the Channel Islands 

 many of the land shells are different from the normal inland 

 type; indeed, there is a named variety of the garden snail. 

 Helix aspersa, which will perhaps some day rise to the dignity of 

 a species. As regards climate, I think there is little doubt that 

 even such causes as difference of rainfall would produce varia- 

 tions in the animal life of a given area. Of course, temperature 

 has a very great deal to do with the variation of species ; this 

 needs no illustration, as it is well seen in the varying fauna of 

 the great zoological divisions of the world. When therefore we 



