20 RETROGRESSIVE DEVELOPMENT IN NATURE. [IX. 



function implies activity, while the use of the hard integument 

 can only be of a passive kind. The horny covering itself is not 

 in the least affected, whether it is useful or useless as a defence 

 against stings and bites : such assaults are quite immaterial to 

 it, nor does its condition in anyway depend upon the frequency 

 or rarity of attack. Degeneration cannot, then, be the result of 

 the protection afforded to the integument. Inasmuch as the 

 integument of all the three kinds of animals mentioned above 

 only degenerates in those parts which are protected by the 

 case, clearly the only explanation must be that the hard cover- 

 ing is unnecessary for those parts which are otherwise 

 protected, and that consequently natural selection has no 

 power to preserve it. 



But the most striking instances are to be found among the 

 social insects, especially the ants. The male and female ants 

 are winged, and at certain times of the year rise into the air in 

 great swarms. Everyone must have seen these swarms filling 

 the air in summer and autumn : they may often be seen on the 

 top of a hill, or surrounding the summit of some tower, alighting 

 on walls and parapets or covering the hats and clothes of people. 

 The males and females, however, form the minority in an ant- 

 community, the greater number being workers — the common 

 wingless ants. Now these workers, in the course of the develop- 

 ment of the species, have forfeited their wings as a consequence 

 of disuse, because the power of flight would be useless to them, 

 and they would be exposed to even greater dangers in the air 

 than on the ground. The business of their lives is to forage for 

 food-supplies, and to collect building materials for the nest, but 

 everything which they seek is obtainable on the ground : they 

 have also to feed the larvae and tend the pupae, and to them 

 alone belongs the defence of the nest if attacked. All these 

 tasks bind them to a life on the ground ; hence, when in former 

 days, they were being gradually developed from perfect females, 

 they came to use their wings less and less, as they gave them- 

 selves up more and more completely to the duties allotted to 

 them. Now, in this case also, it would at first sight seem prob- 

 able that the long continued disuse produced a certain amount 

 of degeneration in each individual, that this first retrograde 

 change was inherited by the succeeding generation, and gradually 

 intensified by further disuse, and so on. Such a view is, how- 



