April, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



403 



adult colour then spread across the head till the whole 

 of the head with the exception of a patch across the 

 front was deeply coloured, the bird now having its 

 head marked similarly to the hen scaup {Fiiligula 

 marila). The final stage was completed by the colour 

 spreading backwards from the beak to join the metallic 

 colours that already existed. 



This case is important for several reasons. Firstly 

 from its analogy with the case of the stoat, where, 

 although the reverse change was in process, yet the 

 parts that in the shoveller were the first to become 

 coloured were in the stoat the last to become white " 



Secondly, to find processes, whose outward effects are 

 so transitory that they can be of no' importance to the 

 individual, practically identical in two animals as 

 widely separated as a carnivorous mammal and an 

 aquatic bird can only {Xjint to one conclusion, viz., 

 that they must have some deep meaning in the internal 

 economy of mammals and birds far transcending their 

 external effect. 



Another point to be noticed is that during the change 

 the birds assumed the more or less characteristic mark- 

 ings of two other species of duck, thus hinting at the 

 probable way in which such markings arose, and, 

 lastly, the assumption of colour on the lines of the 

 " poccilomeres," beginning with the postorbital and 

 ear, and these two joining together and subsequently 

 covering the crown and occiput, while, finally, instead 

 of the colour gradually spreading forwards it started 

 again from near the beak, that is to say on the lip and 

 nose " poccilomeres," whence it covered the head, 

 this, I think, shows that these "poccilomeres" have 

 very real and definite areas, and that although the col- 

 our arising from one " poecilomere " may spread into 

 an area usually fed, so to speak, from another one, yet 

 these " poccilomeres " will always be the first or last 

 patches to be affected. 



It may perhaps be said that the above example is a 

 solitary instance and mere coincidence, but this is not 

 so. The hen tufted duck yearly assumes for a short 

 time during the summer tlie white patch character- 

 istic of the scaup. 



The blackhcaded gull assumes during the early 

 months of the year the brown hood in a very similar 

 manner. The two eye and ear patches show first; 

 these at first tend to join across the head with the 

 crown and occipital patches, forming two dark trans- 

 verse crescents until, finally, the back of the head Ije- 

 comes brown, leaving the frontal patch the last to 

 become coloured. A herring gull, when assuming the 

 white head of summer, becomes white round the beak 

 first of all, and when in the brown plumage of im- 

 maturity will first show signs of the white breast on 

 the sternal [jatch. The bfack throat of the lapwing 

 (Viincllus), W(jrn in sunnner, first appears on the chin 

 immediately behind the lower mandible, and gradually 

 spreads over the neck until it joins the black collar, 

 and in many cases in young birds, e.g., the corncrake 

 [Crcx), the feathers composing the ear patch are the 

 first to grow. 



Lastly I have known a brambling {F. moniifringilla) 

 that, in assuming its black head by abrasion of the 

 feather tips, first lost the brown tips of those leathers 

 round the beak that formed the frontal patch before 

 referred to. This forms additional e\ idence that 

 abrasion takes place on lines similar to those con- 



• I am now able to add a third precisely similar method of change 

 m the assumption of the ecHpse plumage in a smew (see AvkiiU 

 Mag., Feb., 1905.) 



trolling " bleaching," and that it is a process governed 

 by internal conditions. 



This paper deals with a subject of such vast propor- 

 tions and is dependent on so many minute details that 

 it may be well to sum up the results and arguments in 

 a concise form. 



SUMMARY. 



Th(? oljject of this paper has been to show, firstly, 

 that the colour of a bird or mammal is primarily due 

 tO' " activity of nutrition and function," which has been 

 calletl " vigour," and that where conditions lor a high 

 state of " vigour " exist we shall find the majority of 

 animals brightly coloured and vice versa. 



" \'igour " is dependent on two causes. 



(i.) Climate, which contains two factors: — 

 (a.) Temperature. 

 {b.) Food. 

 (2.) Rise and fall of sexual activity. 



In Polar Regions, where the two causes coincide 

 closely, the changes are much more marked and \ iolent. 



In Temperate Regions, where the climate is suffici- 

 ently severe to affect the " vigour," but where, at the 

 same time, there is a sufficiently long period of com- 

 parative plenty to prevent the sexual acti\ity clashing 

 with climate, the changes are less marked. 



In Tropical Regions the first cause is practically re- 

 moved, and any changes in colour are due to sexual 

 causes, except in cases of temperate species which have 

 spread into the south. 



Now the individual " vigour " of various species and 

 groups will differ, and one animal may be able to main- 

 tain a full vigour under conditions which would be 

 impossible to another. This will account for animals, 

 although Polar, becoming brightly coloured, e.g., musk 

 ox, raven, penguin, &c. It follows, therefore, that if 

 they can maintain a full " vigour " in colder regions, 

 they can either (i) maintain an equally full \igour in 

 the tropics, or (2) in hotter climates their metabolism 

 would become too active and they would die. Con- 

 sec|uently, a dark-coloured animal, in Polar regions, 

 must either be confined to Polar regions or be cosmo- 

 politan, e.g., musk ox, raven. 



By a similar process of reasoning, bright-coloured 

 tropical animals will be found extending northwards, 

 probably becoming lighter, \\ hile white or light coloured 

 tropical animals will be confined to the tropics, e.g., 

 tiger, and Rhisomys snmatreiisis, the bamboo rat. 



Seasonal change or migration is a necessity in Polar 

 regions, and birds which migrate to the tropics assume 

 much more g.uidy colours while in hot climates, be- 

 coming dull when the moult takes place mi the Arctic 

 regions, e.g., knot (I'riiiga). 



In temperate regions seasonal change will be a con- 

 stant 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 disappearing, or it may become a 

 " breeding change," as .^eiiiriis caniceps, Cervus cidi. 



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 bleaching 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 the 

 sternum, vent, tip of tail. To these centres or 

 spots the name " Poccilomeres " (spotted part) is 

 given. 



The second part of the paper is devoted to showing 

 how these " poccilomeres " exist as either white or 



