328 REPORTS ON THE STATE OF SCIENCE.—1913., 
I am not certain that this accidental radiation of heat has ever become useful 
to animals, in the fashion in which the production of light, a parallel side issue 
of oxidation, has been turned to account in many groups. I say I am not 
certain, for I remember that heat-radiation plays a part in the relations between 
young warm-blooded animals and their parents, and possibly in the relations of 
gregarious creatures. Long after the heat of the mother has ceased to be neces- 
sary to the feeble young, it remains an attraction. Those who have had expe- 
rience in the rearing and taming of young birds and mammals know how fond 
these are of heat, and how readily they will find their way and attach themselves 
to non-luminous sources of heat, such as the human body, the warm corner of a 
room, or the surface of a radiator. Successive mammalian pets of my own, 
belonging to different groups, have selected the same corner of my dressing-room, 
where hot-water pipes emerge for a few inches on their way to a bath-room, and 
have picked out the same ways of getting to the same radiators. Warmth is a 
surer attraction to a young mammal than food, and if at any time it should 
become more important to the survival of animals that they should have addi- 
tional means of finding their mothers, heat-radiation and the incipient heat-sense 
are ready to be used. 
A few hours before I began to write these words (on a hot day in August) 
my attention was attracted by brilliant points of light in a flower-bed in 
the Zoological Gardens. It was too late in the day and too hot for dew-drops, 
and the points sparkled with an acuter, more coloured scintillation, like diamonds 
of the finest water. I found the source in the ripe blooms of a Solanaceous 
plant (Salpiglossis emperor). The tip of the style was a cross-piece like the arm 
of a crutch, and its upper surface bore a narrow, elongated, and deeply-grooved 
stigma. The sticky exudation formed a brilliant mirror in the hollow of the 
groove, and the curvature of the surface was such that the reflection of the sun 
met the eye as a single, acutely shining point of light. I have never seen any- 
thing more hardly brilliant in a living organism. The flowers were being 
visited by numbers of small flies; they emitted a sickly odour, and their colours 
were conspicuous. I watched for some time, but could not make out that the 
flies were attracted by the shining point, which indeed was visible only from a 
particular angle. They alighted on any part of the corolla and crawled indiffer- 
ently over the inner surface of the flower. Here is a character, startlingly 
definite and conspicuous, and yet apparently only a side issue of the mechanical 
shape of the stigma and the production of the sticky juice. But if it should 
happen that diurnal insects exist which are attracted and dazzled by such a 
shining point of light, as we know that nocturnal insects are attracted by a 
source of light, a lure is there, appearing at the right moment and fully perfected. 
We know that the emission of odours is frequently utilitarian. It is the chief 
means by which insects are attracted to flowers that bloom by night, and the 
plants scatter their perfumes on the air only when ripe for fertilisation. It is 
possible that the odours of the stem and leaves of many plants are distasteful to 
animals, and ward off their attacks. Among animals the emission of odours is 
the chief sexual lure and the awakener of the sexual reflexes, and no doubt it 
serves also to secure recognition between parents and offspring, and amongst the 
members of gregarious tribes. But there are many odours, just as definite and 
characteristic, which we cannot imagine to be useful. Almost every plant and 
the different tissues of a plant, almost every animal] and the different tissues of an 
animal, can be recognised by the sense of smell. I may make a single example. 
In the course of anatomical work I have had to examine the digestive tract of 
many hundreds of birds, belonging to practically every group. It is a curious 
and remarkable circumstance that the intestines offer scents, even to a nose not 
highly skilled, racially or individually, that are almost as characteristic of the 
families as are the patterns formed by the intestinal coils, blood-vessels, and 
mesenteries. The nature of the food, the processes of digestion, the varying 
kinds of putrefaction, all contribute to the result, but the product, so to speak, 
is accidental, and cannot be imagined to have any utility. 
It is with regard to the colour and pattern of living things that the craving 
of the human mind for teleology has led to the greatest excesses. I do not wish 
to suggest that colour and pattern, and the combination of the two sometimes 
called colouration, are never useful. I have no doubt that they serve a purpose 
