PARENTAL CARE 177 



turbots would be much cheaper than they are — the dogfish 

 or skate produce only a dozen or so. But in spite of this fact 

 the dogfish is much more abundant and much more widely 

 distributed than the turbot. Darwin tells us that " no fallacy 

 is more common amongst naturalists, than that the numbers 

 of an individual species depend on its power of propagation." 

 When you have an enormous number of eggs laid they must 

 take their chance, and so great is the struggle for existence 

 that the chance is, at best, a very poor one. A fish producing 

 millions of eggs can exert little maternal solicitude for her 

 numerous brood: "a mother's tender care" is necessarily 

 lacking. But when the fertility is small and the number of 

 offspring few, there is always protection for the eggs and 

 larvae from enemies. 



On the one hand enormous numbers of eggs are produced only to be 

 destroyed, while a few survive to maintain the species; on the other 

 hand few eggs and offspring are brought into the world and all kinds 

 of devices are elaborated for the protection of these. 



Parental care can only be exercised when the number of 

 eggs is small; and it is this maternal or paternal solicitude 

 which enables the species to persist, although the number of 

 eggs may be comparatively very few. A good instance of 

 this is the well-known fish the stickleback, which occurs both 

 in the sea and in fresh water. The male constructs a nest of 

 weeds and twigs fastened together by threads secreted from 

 his kidneys. The nest is a spherical structure with a small hole 

 left on one side for entrance. When it is completed the male 

 seeks out the female and conducts her with many caresses 

 to the nest, introducing her through the aperture. She passes 

 in and lays two or three eggs, and leaves the nest by boring 

 a fresh hole at the side opposite to that by which she entered. 

 The nest has now two doors through which a current of 

 water flows. Next day the male seeks out the same or 

 another female and brings her to the nest, where she lays 

 one or two more eggs. This is repeated till the nest contains 

 a fair number of ova. The male will then watch for a month 

 over the nest, defending it against all invaders, especially 

 against his temporary wives who show a most unnatural 



SI. xs 



