REPRODUCTION AND SEX 



479 



but the reproductive economy is obviously correlated with the high 

 development of parental care. 



W. Kohler has recently taken the trouble to count the eggs in 

 the ovary of a mature stickleback, and found in March 302 that were 

 ripe, and at least as many that were unripe. Three other females 

 contained 100, 200, and 228 ripe or nearly ripe ova — much larger 

 numbers than were previously reported. Since a well-lilled nest 

 contains 120-150 eggs, it seems probable that if the male is poly- 

 gynous, the female is polyandrous. In other words, it looks as if 

 the female must deposit eggs in several nests. And here it may be 



Fig. 65. 



The Three-spined Stickleback [Gasterosteus aculeatus), and its Water- weed 

 Nest, built by the male on the floor of the pool. The head of the female 

 is seen protruding from the nest, in which she hastily deposits a few 

 eggs. 



noted that one would like to know definitely whether the female 

 survives the reproductive strain. Kohler thinks that the unripe 

 eggs observed in March are deposited at a second breeding period 

 in July. He notes that male sticklebacks were seen guarding their 

 nests in July and August, while swimming around them there were 

 half-grown individuals, presumably of the first brood. 



FURTHER ILLUSTRATIONS OF PROBLEMS OF 

 REPRODUCTION 



PARTHENOGENESIS is the development of an egg-cell that has 

 not been fertilised. A familiar case is that of drone-bees, which 



