There should be included here some consideration of one of the most puzzling types of abandonment--the "pregnancy desertion." Attempts have been made to explain it on the ground of the instinctive aversion of the male sex for domestic crises. But the impulse that causes the prosperous householder to move to his club when house-cleaning time arrives will hardly serve to explain such a custom, and as a matter of fact other domestic crises, such as illnesses of the children, do not have any such effect upon the man who habitually absents himself from home before the birth of each child. Other possible reasons for it are the well-known irritability and "difficulty" of women in this condition, and their aversion to sexual intercourse. Some pregnancy deserters take the step in the hope that their wives will bring about an abortion; but this is a modern and sophisticated development and the institution of "pregnancy desertion" is one of undoubted antiquity. Its prevalence among certain European immigrants would almost point to its being a racial tradition. Ethnologists who have studied strange marriage customs, such as the "couvade," ought to turn their attention to discovering the causes of this other and socially more important marital vagary. 10. Temperamental Incompatibility.--It is difficult to catalogue and appraise the causal factors in desertion that lie in personality. They are closely related to differences in background and are intimately involved with the sex relations of the pair. We cannot, however, admit that they are identical with the latter, as some students of the subject claim; or that the only incompatibility in marriage is sex incompatibility. Indeed, two people may be so incompatible as to find in sex their only common ground. The commonest of these temperamental differences center about standards of right and wrong or proper and improper conduct. Especially is this manifested in the bringing up of the children. Extreme self-righteousness on the part of one or the other, nagging and petty criticism, unreasonable jealousy, "sulking spells," violent quarrels, are some of its manifestations. The idea of _possession_ exercised by either of the couple, and especially a tendency to dominate or try to control on the part of the woman, may be a causal factor in desertion. The lack of a saving sense of humor in one or both is often a complicating factor. These comparatively minor differences take on a serious complexion in the minds of the couple; and it is surprising how often a deserting man will give promptly and with every appearance of feeling justified some cause for his desertion which falls clearly under this head. "People forgive each other the big things; it's the little things they can't forgive."