terminal segment in some male Ilemiptera. 421 



PentatomidfB the segment preceding the genital segment 

 is also highly modified for sexual purposes, being greatly 

 diminished in size, and, in fact, differentiated almost 

 entirely for the purpose of forming a remarkably perfect 

 articulation at the base of the genital segment. It is, in 

 fact, in the normal condition of repose, quite concealed 

 between the terminal and the ante-penultimate segments, 

 so that there appears to be one segment less in the male 

 than there is in the female, both on the dorsal and 

 ventral aspects. In some species, — those of the genus 

 Tcsseratoma, for example, — there is a stigma present on 

 this rudimentary segment, proving it to be a true seg- 

 ment, and not a mere articulating ring. 



The extreme difference between the arrangement and 

 general conditions of the male parts in the Pentatomidce 

 and the Coleoptera is, I believe, correlative with a 

 different method of copulation in the two orders. In the 

 Coleoptera it is the rule that the male is placed above 

 the female during coupling, while in the Hemiptera- 

 Heteroptera the general rule seems to be that the male 

 creeps beneath the female : in this latter sex the vulva 

 is invariably placed quite on the under surface of the 

 body, and not in the last segment of the body, but in 

 that preceding it ; and the general arrangement of 

 the parts in the other sex are evidently correlatively 

 modified. 



The most striking of the special features of the genital 

 segment is the peculiar development of the alimentary 

 canal. The chief function of this rectal-cauda is to 

 jn-otect the oedeagus, which lies completely beneath it. 

 For this purpose the under side of the rectal-cauda is 

 hollowed by a large cavity, and the part of this cavity 

 immediately above the cedeagus is reduced to the con- 

 sistency of a delicate membrane ; thus the calibre of the 

 canal of the interior of the cauda is entirely contracted 

 at this spot, so that a very remarkable })rotecting cap 

 for the oedeagus is obtained at the cost of obstructing the 

 canal to such an extent that passage of excrementitious 

 matter can only be made by either depressing the 

 cedeagus or by raising the cauda ott" the oedeagus. 



It appears to be a great comfort or advantage to 

 insects to be able to withdraw and cover over some of 

 the sensitive parts of the body during repose, or when 

 the parts are not in use ; for this purpose a very large 



