At this stage attention should be called to two points. First, that when the details of the geographical distribution of any variable species are studied in that thorough and minute fashion which is necessary for any true knowledge of the interrelations of the several forms, the conception of a species invented by the popular expositions of Evolution under Selection is found to be rarely if ever realised in nature. A species in this generalised sense is an aggregate of individuals, none exactly alike, but varying round a normal type, the characters of which are fixed in so far as they are adapted to environmental exigency. In nature, however, the occurrence of the varieties, and even the occurrence of the variability is sporadic. In one place a population may be perfectly uniform. In another it may be again uniform but distinct. In others the two forms may occur together, sometimes with and sometimes without intergrades. In some localities a sporadic variety may be an element of the population, persisting through long periods of time. In other localities there may be several such aberrations occurring together which are absent elsewhere. Secondly, I would remind the reader that in the light of genetic analysis we know that intergrades, when they do occur, cannot be assumed to represent conditions through which the species must pass or has passed on its way to the extreme and definite forms. Often, perhaps generally, they are nothing but heterozygous forms, and often also they are conditions corresponding with the presence of factors in their reduction-stages. A broad survey of the facts shows beyond question that it is impossible to reconcile the mode of distribution of local forms with any belief that they are on the whole adaptational. Their peculiarities are occasionally the result of direct environmental influence, as we shall hereafter notice in certain cases, but none can attribute such sporadic and irregular phenomena to causes uniformly acting. Writers on systematics, especially those of former generations often conjecture or assert that local distinctions are caused by "differences of climate, soil, food, etc.," in vague general terms. It is usually safe to assume that these remarks do not represent conclusions drawn from actual evidence, for only rarely can they be translated into more precise language. So thoroughly have the biological sciences become permeated with the belief that all distinctions are dependent upon adaptation, that the mere existence of definite distinctions is felt by many to be sufficient ground to warrant an assumption that these distinctions are directly or indirectly due to special local conditions. For example, Dr. J. A. Allen, who has done so much careful and valuable work in delimiting the local forms of the United States fauna, writes of the Ground Squirrels (Tamias)[16] as follows:--