S. A. Arendsen Hein 241 



C. The Beetle. 



1. Secondary Sexual Characters. 



In the literature the following sexual characters are mentioned : 

 for the t/" a stronger thickening of the femur, 

 a stronger curvature of the tibia, 

 a comb-like row of hairs along the inner edge of the tibia. 



When the sexes are compared as to these points it is found that 

 the number of cases in which the first and second differences cannot be 

 stated is much greater than the cases in which that greater curvature 

 of the tibia or thickening of the femur can be observed. It is quite 

 certain that the difference in curvature and thickening is so slight and 

 inconstant that it is unserviceable for distinguishing the sexes. 



In my researches it was of great practical importance to ascertain 

 with absolute certainty the sex of the living beetles. This gave rise to 

 a comparative examination of all the organs and parts of organs in 

 both sexes. The result was satisfactory and only the following three 

 characteristic differences, being the most striking, need be mentioned \ 



a. The Hairiness of the Tibia. 



Over and above the presence of some accumbent yellow hairs in 

 both sexes, the tibia of the cT carries, along the median edge, a row 

 of erect hairs which was never observed in the $ . 



Especially in larger beetles this row of hairs is particularly well 

 developed, and has the form of a comb. 



This row of hairs may however be not very conspicuous and, not 

 seldom, is wanting altogether. When the hairs are present this character, 

 so easy to ascertain quickly is of good service in the separation of 

 the sexes. 



h. The Shape of the last Ventral Abdominal Segment. 

 Referring to Fig. 9 the following facts may be observed. The distal 

 edge of the last or .5th abdominal segment has in the ^ the form of 

 a part of a circle ; in the $ this segment is somewhat sharper and more 

 cone-shaped. Though this difference in the shape of the 5th segment 

 is clearly discernible (after some practice), yet another characteristic 



1 I followed in this research the indications given by Professor Moll as applied to 

 botanical objects, called by him the method of "Pen-portraits," i.e. a scrutiny and 

 description of the structures in their minutest details as far as is observable with the 

 power of the lens chosen for this purpose. (See J. W. Moll, "De beschrijving der 

 simplicia in de Nederlandsche Pharmacopae." Pharmaceutisch weekblad, 1916, Nos. 42, 43.) 



