STRUCTURE, ETC., OF COLEOPTERA. 15 



minute ones, the compound microscope is needed, 

 demanding, nevertheless, much practice and nicety of 

 touch. 



The compound microscope is often, also, indispens- 

 able for the mere superficial examination of exceedingly 

 small beetles ; and such points as the sexual characters, 

 form and number of the joints of the tarsi and palpi, 

 etc., are best seen under it when damped with clean 

 water or benzine. 



The scrutiny of specific characters is at once more 

 general and more close than for any other purpose, and 

 necessitates inspection and comparison of the form of 

 many parts of the body ; the relative length and breadth 

 of joints of the limbs, the degree of punctuation gene- 

 rally, the amount of pubescence, the greater or less 

 elevation, depression, angulation or rounding of the 

 thorax and elytra, the structure of the surface, and the 

 sexual characters, being the chief points to be noticed. 

 Species, also, that resemble each other very much on 

 the upper side frequently differ considerably on the 

 under surface. Occasional differences, owing to want 

 of maturity, accidental abrasion, or slight varieties, 

 the frequent want of similarity in sexes of the same 

 species, and the absolute difficulty of seeing minute 

 specimens in the same light and level, do not tend to 

 decrease the natural difficulties of this branch of the 

 study. 



