Vol. xl.] 90 
forms, where from the nature of the intervening territory 
the species could not exist, and therefore such forms would 
be equally true subspecies, although the intermediate forms 
would not occur. In some cases another factor would come 
in, viz. isolation. A small number cf any species on an 
island would naturally tend to become inbred, and thus all 
individuals of that species would soon tend to bear a family 
likeness and differ slightly from their congeners on a neigh- 
bouring island, and these would be none the less true 
subspecies, although their differences were not directly 
caused by their environment. 
It had been doubted by some whether in Birds and higher 
animals any single individual had changed owing to a 
different environment from oue subspecies to another. Mr. 
Bonhote, however, instanced the case of an Australian Finch 
(Munia flaviprymna), recorded in the ‘ Avicultural Magazine’ 
many years ago by Mr. Seth-Smith*, which, if his memory 
served him right, had so changed after having been brought 
over to this country. Among Mammals (Meriones) he him- 
self had altered the colour in less than six weeks by 
artificially changing the environment, and similar experi- 
ments had also been done in Lepidoptera, southern forms 
having been produced from Arctic forms and vice versd. 
There were, of course, cases that must remain largely 
matters of opinion as to whether a certain form should be 
considered as a subspecies or a good species. The Mourning 
Chat (Gnanthe lugens), in which the sexes of the eastern 
(Egyptian) form were alike, while in the western form 
(GZ. lugens halophila) the sexes were very distinct, was given 
as an example. Mr. Bonhote considered that sexual dimer- 
phism was an essential character, and that as these forms 
differed in an essential character they should be considered 
as different species. As another instance, he said he could 
not agree with a previous speaker in regarding the Pied 
and White Wagtails as subspecies: (1) because the young 
Pied Wagtail assumed its black head in its first autumn, 
whereas the White Wagtail assumed it in the first spring 
* ¢ Ayicultural Magazine,’ vol. v. p. 195 (1907). 
