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 tegmen. 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 tegimen 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 imner 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 
