Anatomy of the Male Genital Tube in Coleoptera. 635 



have not found between Rhynchophora and Phytophaga 

 any distinction that is valid throughout the two divisions, 

 though it is not improbable that an extended study would 

 reveal some important difference. At present the Phyto- 

 phagoidea is by far the largest of the eight series. 



The question as to the distinctness of the series depends 

 largely on the view that is taken as regards " lateral lobes " 

 in Coleoptera. To explain the view we are inclined to 

 take, a digression of some length is necessary. 



It has been suggested that lateral lobes may be modified 

 appendages of the body. We have not found anything to 

 support this view. Indeed if it were so they were doubt- 

 less modified in the precoleopterous stage of evolution 

 and the point would therefore only indirectly concern us. 

 But we incline to another view on this highly speculative 

 point. We suggest that Coleoptera are descended from 

 ancestors in which the efferent ducts from the sexual 

 glands, either as a pair or singly, opened on a membrane 

 connecting the 9th and 10th ventral plates of the 

 abdomen, while the orifice of the alimentary canal was 

 placed immediately above the 10th sternite, which thus 

 separated the two great exits. By slight elongation of the 

 membrane of orifice of the efferent ducts, they were in 

 repose withdrawn within the body cavity ; and a somewhat 

 analogous phenomenon occurring with regard to the 

 rectum, the genital tube and the apex of the rectum 

 became, in the imago, placed inside the body cavity. The 

 10th sternite (between the two parts) shared their invagin- 

 ation so that the external body wall was terminated 

 behind by the apposition of the hind margins of the 9th 

 abdominal sternite with the 10th, or some other, tergite. 

 This apposition, with of course considerable and in some 

 cases very great modifications, has attained so great 

 perfection that sometimes it is very difficult to see 

 any opening at the posterior extremity of the body. 

 According to this view the genital tube is merely an 

 elongation of a connecting membrane between two ventral 

 plates ; the modified 10th sternite either entering into 

 the composition of the tube or not, as the case may be. 

 It may be well here to remark that for the purpose we 

 have now in view, we are mentioning only the simplest 

 aspect of the matter. For our purposes it does not signify 

 how many abdominal segments there were originally, or 

 whether more than one were indrawn either subsequently 



