INSTINCTS OF NEUTER INSECTS. 297 



the matter of way-finding is concerned, seems to me to be 

 this — that in the case of the young cuckoo, and perliaps also 

 in that of certain other migrator}' birds, tlie animals know 

 their way histinctively, or without even one lesson. P>ut if 

 we could ascertain upon what it is that the faculty of homing 

 depends (which, be it observed, is not an instinct, seeing that 

 its occurrence is the exception and not the rule, even in the 

 species which exhibit it), we might very probably get a clue 

 to explain the manner in which heredity has been able to 

 work up this faculty into the instinct of migi-ation. 



No doubt this discussion is most unsatisfactory, and the 

 reason is that we are so much in the dark about the facts. 

 All, therefore, that I have attempted to do is to show that, in 

 the present state of our information, the migratory instinct 

 cannot fairly be quoted as a difficulty in the way of our 

 theory of the formation of instincts in general. And, in 

 order to give emphasis to this statement, I may allude to the 

 general facts already mentioned — viz., that the migratory 

 instinct is both variable and graduated, that it is occasionally 

 exhibited by domesticated animals, and that the sense of 

 direction on which it depends is a very general one among 

 animals, if not also in savage man ; for all these facts tend to 

 show that whatever the causation of the migratory instinct 

 may be, it has probably been proceeding upon the lines of 

 evolution in general. 



Instincts of Neuter Insects. 



Mr. Darwin has pointed out a serious difficulty lying ! 

 against his theory of the origin of instincts by natural selection, j 

 and one which, as he justly remarks, it is surprising that no ^ 

 one should have previously advanced against the well-known 

 doctrine of inherited habit, as taught by Lamarck. The 

 difficulty is that among various species of social insects, such 

 as bees and ants, there occur " neuter," or asexual individuals, 

 which manifest entirely different instincts from the other 

 or sexual individuals, and, as the neuters cannot breed, it is 

 difficult to understand how their peculiar and distinctive 

 instincts can be formed by natural selection, which, as we 

 have seen, requires for its operation the transmission of 

 mental faculties by heredity. The difficulty is increased by 

 the fact that among the termites and many species of ants 



