Anatomy of the Male Genital Tube in Coleoptera. 605 



In the vast majority of cases the median lobe is well 

 developed and quite distinct from the tegnien. In the 

 more generalised (or trilobe) form it is well developed, and 

 more or less tubular, with the median orifice situate on 

 the distal extremity, and the median foramen at the 

 basal extremity. In many trilobe forms it is articulated 

 to the lateral lobes by a more or less distinct condyle on 

 the dorsal side of the median foramen ; in such cases the 

 first connecting membrane {cm 1) is short, and the median 

 lobe can only turn upon its point of articulation {'pa). A 

 pair of median struts are often attached to the base of the 

 median lobe to give support to the muscles that actuate it. 

 In the Scarabaeidae the median lobe is comparatively 

 reduced in chitinisation, and often in size, and in the more 

 highly evoluted forms the tegmen entirely envelopes and 

 conceals it. In the Tenebrionid type the reduction of the 

 median lobe reaches its maximum ; in some of their forms 

 it is only represented by a small membrane on which 

 the median orifice is placed. The line of evolution of the 

 median lobe in the Staphylinidae is from a tubular form, 

 with a basally placed median foramen, to a bulbous form, 

 with the median foramen placed nearer to the median 

 orifice. This reaches its maximum development in Xantho- 

 linus. In the Cucujoidea group and in the Phytophagoidea 

 the median lobe is generally tubular (at any rate on the 

 distal portion), and the first connecting membrane long, 

 so as to allow the median lobe a large amount of play 

 through the more or less ring-like tegmen. 



The tegmen, in the more generalised groups, consists of 

 two parts, the basal-piece, and a pair of lateral lobes. The 

 chitinisation of the basal-piece then often forms a shield- 

 shaped plate on the ventral aspect, the dorsal aspect being 

 membranous. Unless the chitinisation forms a complete 

 tube the membranous dorsal part and the second connect- 

 ing membrane are indistinguishable. The lateral lobes in 

 their generalised form consist of a pair of more or less 

 pointed lateral organs, their outer surface being continuous 

 with the basal-piece, their inner surface connecting to the 

 base of the median lobe, and their position being that they 

 lie one on each side of the median lobe. 



In position, size and form the lateral lobes differ so much 

 in various families that their true homology in the different 

 groups will probably be only settled after tracing their 

 modifications through long series of forms, and by studying 



TRANS. ENT. SOC. LOND. 1912. — PART III. (DEC.) SS 



