772 ; rEporT+1899; 
vides the mechanism by which organisms are able to vary, independently of the 
conditions in which they live. It lies, therefore, at the very root of the evolution 
problem; the power of combining to form a zygote is one of the fundamental 
properties of living matter, 
Species. 
Now let us consider one of the effects of this property upon organisms, The 
effect to which I refer is the division of animals into groups called species. Species 
are groups of organisms, the gametes of which are able to conjugate and produce 
normal zygotes. Now in Nature there appear to be many causes which prevent 
gametes from conjugating. First and most important of all is some physical 
incompatibility of the living matter which prevents that harmonious blending of 
the two gametes which is essential for the formation of a normal zygote. Very 
little is known as to the real nature of this incompatibility ; in fact it is hardly an 
exaggeration to say that nothing is known. It may be that there is actual 
repulsion between the gametes, or it may be in some cases, at least, that the 
gametes are able to fuse, but not to undergo that intimate blending which is 
necessary for the production of a perfect zygote. In some cases we know that 
something like this happens; for instance, a blend can be obtained between the 
horse and the ass, but it is not a perfect blend, the product or zygote being imper- 
fect in one most important particular—namely, reproductive power, 
A second cause which prevents conjugation is a purely mechanical one—viz. 
some obstacle which prevents the two gametes from coming together. As an 
instance of this I may refer to those cases amongst plants in which conjugation is 
impossible, because the pollen tube is not long enough to reach the ovule. In yet 
other cases conjugation is impossible because the organisms are isolated from one 
another either geographically or in consequence of their habits. There are probably 
many causes which prevent conjugation, but, whatever they may be, the effect of 
them is to break up organisms into specific groups, the gametes of which do 
normally conjugate with one another. 
In many cases, no doubt, the gametes of organisms which are kept apart in 
Nature by mechanical barriers will conjugate fully if brought together. But in 
the great majority of cases it is probable no amount of proximity will bring about 
complete conjugation. There is physical incompatibility. Here is a fruitful 
opening for investigation. Observations are urgently needed as to the real nature 
of this incompatibility. 
Importance of the Study of Variation, 
Another and most important effect of conjugation is, as we have seen, the much- 
spoken-of constitutional or genetic variations. They are,as we have already insisted, 
of the utmost importance to the evolutionist. Evolution would have: been impos- 
sible without them, for it is made up of their summation. It becomes therefore desi- 
rable to find out to what extent a species is capable of varying. This can only be 
done, as Mr. Bateson has pointed out, by recording all variations found. Mr. Bate- 
son, in his work already referred to, has carried this out, and has shown the way — 
to acollection of these most important data. In order to carry it further, I would 
suggest that the collection be made not only for structure, but also for function. 
This has been done largely for the nervous functions by psychologists and natural- 
ists who pay special attention to the instincts of animals; but we want a similar 
collection for other functions. [or instance, the variations in the phenomena of 
heat and menstruation, and of rut amongst mammals, and so on, To do this is 
really only to apply the methods of comparative anatomy and comparative 
physiology to the members of a species, as they have already been applied to the 
different species and larger groups of the animal kingdom. Such investigations 
cannot fail to be of the greatest interest. Indeed, when we have learnt the normal 
habits and structure of a species, what more interesting study can there be than 
the study of the possibilities of variation contained within it? Then when we 
know the limits of variability of any given specific group, we proceed to try if we 
