<><> ANTS. 



an even more surprising range of intraspecific variation in the number 

 of faeets. The degeneration of the lateral eyes in the workers has pro- 

 ceeded furthest in the African drivers (Dorylits ) and American legionary 

 ants (licit nn i. In the former the eyes have disappeared completely, 

 and the same is true of certain species of liciton, hut in many of the 

 latter each eye is reduced to a single facet, which, however, is no longer 

 connected with the brain by an optic nerve. At any rate, in the >peci- 

 mens of /:. scliinitti, which I sectioned, I found the vestigial optic nerve 

 reduced to a small thread depending freely from the inner surface <>f 

 the eye at some distance from the optic lobe. In some species of Eciton 

 and .linictiis the eyes are represented only by a pair of small, pale dots 

 in the chitinous cranium. \Yhile the females of all these genera have 

 no better eyes than the workers, these organs in the males are extremely 

 large and contain many hundreds of ommatidia. It is obvious, of 

 course, that such enormous differences in the size and development of 

 the lateral eyes in different species and in the various castes of the same 

 species must imply corresponding visual differences. 



The Median Eyes, or Stemmata. These occur in the males and 

 females of nearly all ants and in the workers and soldiers of a number 

 of genera. They are largest in the males and always of very small size 

 in the workers. In the male Dorylii, Ecitonii and Ponerinse they are 

 unusually well developed. In general, it may be said that they tend to 

 vary in correlation with the lateral eyes: the better these are developed, 

 the larger are the stemmata. Structurally the latter cannot be derived 

 from a simple type of sensilla, like that to which we have referred 

 the lateral eyes and the other sense-organs above described. On this 

 account some authors believe that the stemmata are unique and ex- 

 tremely ancient organs, i. c., relicts of eyes that preceded the lateral eyes 

 in the phylogeny of insects. It should be noted, however, that both 

 lateral eyes and stemmata present the same development in the earliest 

 known fossil insects, the Carboniferous Palseodictyoptera, that they do 

 in recent species. The stemmata are supposed to give an indistinct 

 visual image of very near objects. Further consideration of the func- 

 tion of these and the other sense-organs briefly described in the pre- 

 ceding paragraphs is reserved for a future chapter. 



