IXTHODUCTION. 



15 



vertex of the head in many beetles. There is darker pigment 

 also at the edges of plates, especially wlieretwo edges have united, 

 forming a highly chitinised suture, and this often remains as a 

 dark line wlien all other trace of the suture has vanished. In- 

 crease of the amount of pigment produced results in the dilatation 

 of these colour-patches and their fusion in a variety of ways. 



Sexual Dimorphism. 



Tlie present subfamily is not, like the Dy^tastin^, the Coprin^, 

 and the Lucanid^e, a group in which dimorphic forms are pre- 

 dominant. Highly developed armatures, such as are familiar in 

 those groups, are here found in a very few cases only ; but,, 

 although not in its most exaggerated forms, Sexual Dimorphism 

 can be studied with special advantage in the Eutelin^e, for 

 there is perhaps no group of similar size in which it manifests 

 itself in a greater variety of phases. This applies in a special 

 degree to the Oriental representatives. 



Fig. 4. — Extremity of tlie body of : a, Anomala (ventral side), female ; b, ditto,, 

 male : c, Adoretus (lateral view), male ; d, ditto, female. 



In larger genera like Anomala and Adoretus, in whicli the species 

 are .very numerous and difficult to distinguish, it often happens 

 that the two sexes of the same insect, although not differentiated 

 by any obviously sexual features, like the horns or mandibles in 

 the other groups just mentioned, resen)ble each other less than 

 they do specimens of the same sex of closely allied species, and it 

 is therefore of great importance to know with certainty the sex 

 of the example it is desired to identify. The sex-nuirks in the 

 subfamily are very many and various, and some, like division of 

 the claws, may indicate the male in one case and the female in 



