CORRESPONDING SOCIETIES. 329 
in the interplay of the sexes, that they are useful in the various fashions 
described by Darwin, Poulton, and Abbot Thayer, and that they have played a 
large part in the success and failure of races. But I wish to remind you that 
they are inevitable outcrops of the structure and physiology of living organisms, 
and that, howsoever they may have been altered under the agency of natural 
selection and sexual selection, they must have existed and will exist so long as 
life endures. 
Pattern is essentially a repetition of parts, and is the result of the mode of 
growth of organisms. A few scraps of tinsel and coloured glass placed in the 
well of a kaleidoscope form indefinitely varying patterns as the tube is revolved 
and they fall into different places. The geometrical patterns are formed by the 
reflections from a set of mirrors in the bottom of the tube, placed so ae to 
multiply the images. Jf irregular holes be torn in a sheet of paper that has been 
doubled and redoubled, a symmetrical pattern is visible when the sheet is un- 
folded. Growth of tissues takes place by the multiplication of cells, cell-masses, 
organs, and parts of tissues and organs, for there is a physiological limit to 
increase in size of the different units of the body. Thus repetition patterns occur 
inevitably, producing the various kinds of symmetry, radial, concentric, 
metameric, antimeric, and so forth, which are characters of living things so 
conspicuous that even the untrained eye at once distinguishes a fossil in the 
rocks or a shell on the sand from its contrast with the formless monotony of 
surrounding matter. 
The multiplication or repetition of cells or parts may take place regularly, 
radiating in every direction from the growing point, until the product of one 
centre of growth is modified by the different conditions it meets on different parts 
of its periphery, by interference with the products of other centres of growth, 
or by the changed conditions of nutrition brought about by its own growth. 
Growth in one plane or radius may be arrested, in others proceed with greater 
vigour; so that annual systems spread out into curving streaks, like the stream- 
lines on the surface of muddy water, or it may be subjected to local, temporary, 
or seasonal intermittences, with a consequent elaboration of pattern. In its 
finest details and its gross structure every organism displays pattern. 
When the microscope reveals the exquisite sculpturing on the surface of a 
scale, the graceful details of the cross-section of a stem, or the intimate beauty 
of tissues like brain, or liver, or kidney, we are not tempted to explain the 
patterns on utilitarian principles. We propound no theory of mimicry, or of 
protection, or of sexual advertisement, but are content to accept their presence 
as an organic fact. But when the erowth patterns reveal themselves on the 
surface as the markings on a shell, the stripes on a skin, or the vermiculations 
on a feather, the craving for teleology is aroused. JI do not doubt but that these 
natural patterns have provided material for selection, but chiefly in the sense 
that they have been obliterated where they were visible. No assemblage of living 
animals shows externally visible growth-pattern in a more conspicuous fashion 
than the members of the abyssal fauna, where the only light is a dim and fitful 
phosphorescence, and where conspicuousness can be attended with no dis- 
advantage. 
Organisms, like all visible things, must have colour, and it is still less neces- 
sary than in the case of pattern to suppose that the colour as such subserves a 
useful purpose. We do not ask what advantage it is to one form of carbon that it 
should be black and opaque, to another that it should appear a crystal of the 
rainbow, why calomel should be white, mercuric iodide scarlet, or what gain it is 
to the sea that it should display its deepest azure when we are shivering under 
the blast of the mistral. Many of the most brilliant colours, the shifting metallic 
sheens, are the direct result of structure. The incident light is broken up when 
it is reflected from a sculptured surface, as in the case of the shining glow of a 
pearl, the inner face of a shell, and the shifting brilliance of a rifle-bird’s throat, 
or by reflection from an opaque surface through a transparent layer, as when the 
swim-bladder or the sheath of a tendon display the shivering hues of a mirror of 
polished silver. The pearl grows as a disease of the tissues of the oyster, hidden 
away from light, not revealing itself until the animal, dredged up from the 
bottom of the sea, has rotted into a putrid mass. The internal tissues of every 
creature reveal a multitude of iridescent surfaces only when the dissecting knife 
