THE CYCLE OF SEX 133 



emergence of maternal care, as if the mother 

 was loath to part with these eggs or offspring 

 which she has created, for it has long been 

 recognised that the care of the young is like 

 a prolonging of gestation. Where the off- 

 spring are very numerous, as in fishes with 

 their tens of thousands, there is neither need 

 for nor the possibility of parental care; as 

 fertility diminishes the possibility of parental 

 care increases, the mother's energies are less 



FIG. 20. Female Spider iJoiomedes xnira bills carrying 

 underneath her body, attached by silk threads, the 

 silken cocoon containing the eggs and eventually the 

 young spiders. (Alter Black wall.) 



terribly exhausted, and the need for care 

 also increases. There is a much smaller 

 margin for contingencies. And the better 

 the nurture, conversely, the more the number 

 of the offspring tends to be reduced. Thus 

 the bird that spends time in making a very 

 secure and finely finished nest an expression 

 of its own high individuation may very 

 successfully hold its own as a species with 

 a small clutch of eggs produced once a year. 

 Similarly in mammals, the long gestation and 



