CORRESPONDING SOCIETIES. ooo 
by unequal growth, areas belonging to one segment occasionally have invaded 
neighbouring territory, and the primitive regularity has become disguised, and 
tends to be more and more disguised in the course of ontogeny and phylogeny. 
In such anatomical and physiological facts we must seek for the origin of the 
primitive patterns of mammals. No doubt in many cases they have been retained 
and perhaps accentuated by selection. But selection does not and cannot 
account for their origin. It seems to me in many cases incredible that they 
are utilitarian. In the young of many animals, they may serve for protective 
concealment, but they occur almost with equal frequency on the least visible 
portions of the body, on the under parts and legs, and in the case of creatures 
whose young are carefully hidden and sedulously guarded by the parents. The 
general trend of events seems to be the obliteration of these primitive patterns, 
and their replacement by an even tone. The even tone, in its turn, is being 
replaced, especially in the males, by countershading, and by many of the odd 
and brilliant patches and marks which may be interpreted as decorative sexual 
colouration or as ruptive, outline-breaking patterns. Where the young are 
neither striped nor spotted they are more uniformly coloured than the adults, 
and slowly acquire the adult condition, the females more slowly than the males. 
The trend of events in birds is similar but not identical. The kind of 
plumage most common in the lower types of birds and that appears most 
frequently in young birds is a rather uniform dull brown or grey, marked with 
patterns of stripes and spots and mottlings symmetrically arranged with regard 
to the whole body and to the individual feathers. Many of these primitive 
patterns and colourations suggest the accidental expression of structure, and can 
be imitated in a very close fashion by mechanical means. Certainly they appear 
to serve for protection, and blend with rough and mottled backgrounds in a very 
complete fashion. But, just as in the case of mammals, they often occur on 
parts of the body not naturally the most exposed, or in cases where protection is 
secured by other means. At first the plumages of the young and of adult males 
and females were similar and retained throughout the year. Next, during the 
breeding season, the males began to assume brighter colours, and when the breed- 
ing season was over, relapsed into the duller ancestral plumage, passing into the 
condition usually spoken of as ‘eclipse.’ In such a stage, the males in eclipse, 
the females and the young were all much alike, and there are many birds in which 
this condition is retained. A later modification came about when the females as 
well as the males began to assume brighter tints in the breeding season. When 
the breeding season was over, males and females both went into eclipse, with the 
result that males and females in eclipse, and the young in their early plumage, 
were all much alike, and wore a plumage recalling the ancestral condition. 
This stage persists in a large number of cases. Then the period during 
which the breeding plumage was retained became longer and longer, half the 
year in some of the weaver birds, for all but a few weeks in the game birds and 
in most of the ducks, or for the whole year, as in South American ducks, king- 
fishers, and parrots. Every stage in the suppression of the eclipse or ancestral 
plumage still exists; in some of the game birds and tanagers, for instance, it 
is represented only by a few feathers. When the eclipse plumage has been 
suppressed, only the young birds retain the dull ancestral livery, and there are 
many cases in which even the newly fledged birds, or birds in the first down, 
show traces of their future brilliancy. 
I have attempted not to weary you by going into much detail. I have been 
trying to show you that amongst birds and mammals there has been a general 
chenge from dull colours and mechanical patterns to brilliant and fantastic 
garbs, an intermediate stage of almost uniform colouration having been passed 
through. The process has been an inevitable outcrop of organic growth, a naive 
blossom of the tree of life, as free from purpose as art is free from morality. It 
has been associated with an increase in the vigour of the body and a heightening 
of the vital activities, so that growth, respiration, and excretion, and all the 
chemical changes in the living laboratory, have become more exuberant. It is 
natural, therefore, to find the beginnings of more brilliant colour and more 
aberrant growth associated with the breeding season, for it is then that the 
strength and vigour of the animal hody are most acute. No doubt there were 
critical stages during which natural selection played a great part; most notably 
