S. A. Arendsen Hein 237 



c. This 12th segment has in the </ a cup-shaped dint ; this dint 

 is in the $ either absent or much less deep, and indistinct. 



d. The tissue of the segments, dimly seen through the chitinous 

 skin, has a dull creamy-yellow colour in which in the Uth segment 

 of the cT. to the left and right of the median-line, is seen a peculiarly 

 curved figure, the concavity of which is directed laterally. Both figures 

 lie symmetrically to each other, and have a semi-opaque grey colour, 

 like an oil-stain on white paper. 



In the $ these paired figures meet in the median-line of the 11th 

 segment, and continue unpaired distally ; the whole figure has the 

 shape of a two-pronged fork, with a short handle, thickened in the 

 form of a ball while the opening of the fork is directed proximally. In 

 the (^ this fork -figure is lacking. 



By means of these four characteristics, of which the first is the 

 most distinct and preferable to all others, the investigator will always 

 be able to determine the sex with absolute certainty. 



The above-mentioned sex-differences make it not only possible to 

 isolate male and female beetles before their emergence, but they also 

 provide a means of answering the following questions among others : 



(a) Is the number of males and females alike or does either of the 

 sexes predominate ? 



(/S) Is there any difference in the average length of the female and 

 male beetle, and, if so, what is the proportion ? 



2. The Ratio of the Sexes. 



In the course of 8 months 3000 pupae were examined as to sex, 

 and after that, measured. These pupae belonged to one group, being 

 a mixed population brought together from different places in Holland. 

 They were obtained and measured in the following months: 



The 1st thousand from the 2nd of April — 3rd May 1915. 

 The 2nd thousand from the 4th of May — the 4th of June. 

 The 3rd thousand from the 5th of June — the 28th of June. 

 The sex ratio of this group was as follows : 



Number 



