288 THE BIOLOGY OF BIRDS 



kept for a longer time in association with the mother, or with 

 both parents, it became possible for the parents to know 

 their own children and physical bonds of tenderness were 

 established. Thus parental care worked in favour of its 

 own further evolution. The family reduced to small di- 

 mensions and kept for a longer time in touch with the parents 

 not only engendered parental affection in the individual, 

 but formed the sieve by which germinal variations in the 

 direction of more parental affection were sifted, thus lead- 

 ing to the evolution of racial virtues. This is one of the 

 indirect ways in which mind may act as a factor in evolution. 



§ I. Incubation 



Some of the lower Vertebrates (fishes and amphibians) 

 remain in close association with their eggs or keep them in 

 contact with their body. The gunnel on the shore coils 

 round its egg-mass, the male sea-horse carries the eggs in a 

 ventral pouch and the male Kurtus in a double bunch on 

 the top of his head. The Surinam Toad carries her develop- 

 ing eggs in skin pockets on her back ; Darwin's frog {Rhino- 

 derma darwini) carries the eggs, few in number, in his 

 mouth. These are instinctive habitudes, but they are 

 probably associated with some degree of awareness ; it is 

 difficult to think of them originating without this, though they 

 may eventually become matters of instinctive routine. In 

 some Boidae the mother snake coils round her eggs and this 

 approaches incubation. 



It is natural that the female bird should rest after the 

 exhaustion of egg-laying, and it may be that the nest has in 

 some cases a primary association with the act of mating, but 

 it seems an unworkably extreme view to refuse the brooding 

 bird any appreciative awareness of the eggs as products of her 

 own being. It is certain, of course, that the incubation has 

 become part of instinctive routine, engaged in because of 

 inborn nervous pre-arrangements which operate when 

 appropriate stimuli pull the trigger ; but it is uncertain to 

 what extent the instinctive performance is associated with 



