SPECIES

chiefly used as a term in natural history. In the attempt to study life in its infinite variety, grouping according to similarity is a nece ary scientific proce , and a first division gives the cla , which is subdivided into orders; an order contains groups, each of which is a family; this again is grouped into genera, each genus into S., while a S. is grouped into varieties. The primary grouping is nece arily by means of very fundamental differences, but as we proceed they become le fundamental yet perhaps more compiex and ‘aifficult of discrimination. ‘The theory of evolution and the great impetus it gave to the study, not of mere apparent differences but differences of development from the germ, has made cla ification more certainly determinable, and shows what e entials distinguish between groups. Thus, the distinguishing features of a S. are not merely observed in the individuals but in generation after generation of them. ‘Thus, mere acquired characteristics due to environment are insufficient grounds for distinction of S., though the transmi ion of such—a much disputed point—might if it took place and persisted, give rise to new 8. This persistence of the distinguishing features is very difficult to determine in extinct 8. when fo ils are not numerous, and leads to difficulties in cla ification. At present the cla ification, generally, is one largely of convenience and consensus of opinion in deciding what differentia are to be selected. It has been common, and is still, to consider different 8. determinable by infertility the one with the other, although hybrids are becoming more and more common with increased knowledge. The white, black, and yellow races of mankind have many differentia, yet are considered varieties of one S. One method of convenience is to arrange a genus according to certain characteristics simply statistically, and consider the best marked groups as S.; there are in any case examples difficult to group, failing as it were equidistant between groups. From the point of view of evolution it seems probable that S. have largely arisen from infertility, but largely because persistence from generation to generation is so often chosen as a reason for deciding the characteristic. If from any parentage we examine the offspring, great variations are observed, and experience in estimating the degree of such family variation is useful in deciding whether characteristics are sufficiently marked to warrant grouping in 8S. The differences between S. should always be greater than those found in offspring from the same parentage. In spite of all guides, the greatest students are often in disagreement as to the number of S. in a genus. The question of the origin of S. occupied the attention oi naturalists very largely during the early part of the 19th century, and culminated in Darwin’s theory of natural selection and survival of the fittest. Of very great moment is the question of transmi ion of acquired characteristics, on pee authorities are yet in disagreement. 3