the male possesses certain organs of sense or locomotion, of which the female is quite destitute, or has them more highly developed, in order that he may readily find or reach her; or again the male has special organs of prehension for holding her securely. These latter organs, of infinitely diversified kinds, graduate into those which are commonly ranked as primary.[4] [4] Darwin, _The Descent of Man_, 1877, p. 207. The female, on the other hand, in addition to those sexual characters which are strictly primary, has “organs for the nourishment or protection of her young, such as the mammary glands of mammals, and the abdominal sacks of the marsupials.” In addition to these she is frequently provided with organs for the defence of the community; for instance, “the females of most bees are provided with a special apparatus for collecting and carrying pollen, and their ovipositor is modified into a sting for the defence of the larvæ and the community.” We are assured by Mr. Darwin that many similar cases could be given.[5] [5] _Ibid._, p. 208. Here, then, with almost the first or primary step toward sexual differentiation, may be observed the establishment of that peculiar bias which upon investigation will be seen to extend all along the two lines of sexual demarcation, and which (to anticipate the conclusions of our argument), as soon as mankind is reached, appears in the male as extreme egoism or selfishness, and in the female as altruism or care for other individuals outside of self. We are assured, however, that it is not alone to the reproductive organs and their functions that we are to look for the chief differences in the constitution and character of the sexes. Neither is it entirely to Natural Selection that we are to seek for the causes which underlie the specialization peculiar to the two diverging lines of sexual demarcation; in addition to primary sexual divergences, there are also “secondary sexual characters” which are of great importance to their possessor. Indeed, from the prominence given to Sexual Selection by Mr. Darwin, it would seem that it played a part in the development of males quite equal to that of Natural Selection itself. Now the difference between Natural Selection and Sexual Selection is that, whereas, in the former, characters are developed and preserved which are of use to the individual in overcoming the unfavourable conditions of environment, by the latter, only those characters are acquired and preserved which assist the individual in overcoming the obstacles to reproduction; or, to use Mr. Darwin’s own language: