72 COLEOPTERA. 



But it must be observed that the hooked hinder tro- 

 chanters, and excess of clypeal emai'gination, are purely 

 sexual characters; the female of rusimtor having the tro- 

 chanters terminating in short spines, and the emargination 

 of the clypeus small, triangular, with the apex rounded, 

 and only extending about half-way up. Thus it is to be 

 expected, by analogy with other known instances of sexual 

 dimorphism, that a small undeveloped male of riispator 

 would exhibit all these points of degradation, and assume 

 the female form ; and it is precisely such an insect that I 

 believe the microcephalus of Thomson to be. If I needed 

 any evidence, beyond that of analogy, to confirm this idea, 

 it would be afforded by the fact that I captured at Rannoch, 

 in June last, males of undoubted ruspator in company with 

 a male intermediate between their full development and the 

 degraded foi-m of Thomson's niio^ocephalus. 



With regard to the females of rnicrocepjhaluSy I believe 

 that they are simply small females of ruspatoi^ ; in which the 

 diminished size is accompanied by a corresponding diminished 

 condition of the marks of sexual difference, which are cer- 

 tainly liable to variation in other insects. 



The following are a few instances in which a modification 

 of the differential characters of the male occurs, so that small 

 specimens of that sex often resemble the female : — Necrodes 

 littoraUs (inflation of hinder femora) ; most of the genus 

 Anhotoma, and especially cinammomea (development and 

 toothing of hinder femora, curvature of hinder tibiae, &c.), 

 wherein there are nearly always three distinct forms; Colon 

 (length of curved spine to hinder femora) ; Agathidium 

 (development of left mandible, and of the horn often existing 

 on it) ; Liodes (spining of posterior tibia, and dilatation of 

 front tarsi) ; Creophilus and Lucanus (development of head 

 and mandibles) ; many Philonthi (development of head and 



