( clxxxvii ) 



(Megachile spp.) need and possess jaws modified to act as 

 " scissors " and also as " chisels " or " gouges." "Wasps procure 

 material for the " paper " of which they form their cells by 

 gnawing off and carrying away fragments of wood from posts 

 and palings, etc., etc. Many of these entirely $ occupations 

 require not only special development of the mandibles, but of 

 the muscles which move them, and consequently of the size of 

 the whole head : and of this we find frequent instances both 

 in Bees and Fossors (spp. of Osmia, certain Halicti, many 

 Scolia and Cerceris and Fhilanihus spp., etc.). It is, however, 

 only by exception that the characters actually become 

 pai'adoxical. 



Another cause tending perhaps in some cases to increase 

 the size of the $ head, is a greater development of the hrain 

 in that sex, corresponding to the much greater complexity 

 and variety of the 9 instincts. Ants, whose $ $ (as compared 

 with their 5 ?) are generally " microcephalous idiots," may be 

 a case in point. The following fact is curious and apparently 

 isolated. I cannot explain, but ought not to ignore it. The 

 female only of a single Cerceris (komarovi) has the back of 

 the head, behind the eyes, armed with a thorn-like tooth. 

 Something similar occurs in males only of a Crabronid sp. 

 (a Lindenius), and in both sexes of another Crabronid 

 {^Hoplocrahro quadrimaculatus) . 



The curious elevation and projection of the clypeus in 

 certain Cerceris 9 ? {ferreri, labiata, conigera, etc.), suggesting 

 sometimes a pick and sometimes a spade or shovel, seem 

 likely, as well as the adaptations of mandibles already men- 

 tioned, to assist the insects in their digging operations. The 

 same may explain the so-called '^ horns " on the faces of some 

 5 Osmiae {rufa, tricornis, etc.). 



(3) The legs of $ Aculeates show in various groups 

 characters which obviously indicate the special industries of 

 $ ? in that group, but generally consisting rather in modifica- 

 tions of the pilosity ("spines" as well as "hairs" being 

 included in that term) than of the actual shapes of joints, 

 such as we have encountered in the case of many males. 

 Beginning with Industrious Bees, we have a number of 

 Genera in which the actual leg-joints differ little in the sexes, 



