186 ME. J. L, BONHOTE ON 



lighter, while white or light-coloured tropical animals will be 

 confined to the tropics; e.g., Tiger, and Rhizomys sumatrensis, 

 the Bamboo E-at. 



Seasonal change or migration is a necessity in Polar Eegions, 

 and birds, which migrate to the tropics, assume much more 

 gaudy colours while in hot climates, becoming dull when the 

 moult takes place in Arctic Regions, e.g. Knot {Tringa). 



In Temperate Regions seasonal change will be a constant 

 feature, but the changes will not be so marked, e.g. Squirrel, 

 Deer; but when these animals reach torrid zones, the " seasonal 

 change " will tend to persist for some time, gradually dis- 

 appearing, or it may become a " breeding change," as in Sciurus 

 ccmiceps, Gervus Midi. 



There is among mammals and birds a process known as 

 "bleaching; " this, I attempt to show, is an active process, and 

 not mere action of wind and weather. 



I further show that hleacMng always takes place along certain 

 lines, starting and spreading in various degrees from certain 

 centres ; e. g., lips, eyes, ears, crown of the head, occiput, 

 shoulders, thighs, fore end of sternum, vent, tip of tail. To 

 these centres or spots the name " poecilomere " (spotted part) is 

 given. 



The second part of the paper is devoted to showing how these 

 " poecilomeres " exist as either white or deeply-coloured patches 

 throughout the majority of species of Mammals and Birds : 

 sometimes as large and conspicuous patches, e. g. hind-quarters 

 of Eabbit, rump of Bullfinch ; and at other times only dis- 

 tinguished from the surrounding parts by difference of shade so 

 slight as to be incapable of serving any warning, protective, or 

 other similar purpose. 



It is then pointed out that in some cases the " poecilomeres " 

 are only visible as transitory patches during the time an animal 

 is undergoing a change of colour. 



The head of the Stoat and of a young Shoveller drake are 

 cited, amongst others, as examples of the change taking place 

 along precisely similar lines, whence it is argued that as the out- 

 ward effect is so slight and transitory, and as the process exists 

 in two animals so widely separated, the fundamental cause must 

 be a deep-seated physiological one. 



I therefore claim to have shown that where conditions for 



