Recapitulation. 135 



duces the nut-galls so important in the manufacture 

 of ink. Another species attacks the rose, arid a sin- 

 gular gall-fly has a cuckoo-like habit of laying its 

 eggs in the galls formed by other insects. 



The ants are probably the most intelligent of insects, 

 having the most complex social organisation and pos- 

 sessing the most complex nervous system in proportion 

 to their size of any invertebrate. The males and 

 females are winged, the workers are wingless, and their 

 sting gland secretes formic acid, the material whereby 

 they irritate or sting. No group of animals are better 

 worthy of study, and their house-building and polity, 

 slave-holding, aphis-cow-keeping, and other habits 

 have long been favourite subjects of observation with 

 entomologists. 



The ants form a fitting termination to the Inverte- 

 brata, as in intelligence and in interest they may be 

 looked on as bearing to the other invertebrates some- 

 thing of the relation which man has to his neighbour- 

 ing vertebrates. 



Recapitulation. The sub-divisions of insects are 

 by some looked upon as deserving of a higher than 

 ordinal rank, but as the nature of a group depends on 

 the nature of the range of organic structure in the forms 

 comprehended therein, and not on the number of in- 

 cluded individuals, we cannot but see that, in each 

 order of insects, the component species are constructed 

 so much on one type as to forbid us from making of 

 them more than ordinal groups. 



The orders of insects which we have briefly 

 noticed may be summarised as follows : 

 A. Insects with imperfect or no metamorphoses. 



