Anatomy of the Male Genital Tube in Coleoptera. 601 
branch proceeds to each testis. In a peculiar structure of 
this kind it is evident that the homologisation of the parts 
is attended with some special difficulties. Extensibility 
and retractibility of the tube are carried to an extraordin- 
ary perfection, and the length of the tube is in some cases 
enormous compared with the size of the creature, and yet 
the “orifice” may in one position of the organ be placed 
near the distal, in another position near the proximal 
extremity. The same “orifice” is in fact at one moment 
of the creature’s existence placed inside and quite near to 
the centre of the body, while at another moment it may 
be placed far away, at the extremity of the extended tube. 
The walls of this protean structure become in some places 
hard, and form sclerites. The study of these sclerites is 
one of the chief aids in our endeavour to understand the 
changes the tube may have undergone during its evolution. 
The homologies of the various parts of the male genital 
tube are, within certain limits, very easy to follow, and 
even in some of the most extreme forms can be made out 
by anatomical comparison. But beyond the limits we 
have alluded to, the questions become very difficult, and 
will really only be settled by studies of the ontogeny that 
at present are not forthcoming. As misconception has 
been, and still is prevalent to a considerable extent, there 
are a few general points to which we must allude. Accord- 
ing to our view the genital tube commences where the 
body wall ends. Anatomically it is not easy to decide 
where that spot is, because body wall and genital tube 
are continuous. 
Embryologists consider with good reason that the 
stomodaeum and proctodaeum are the poles of the body 
wall, therefore all parts that have their origin on the 
dorsal aspect of these openings are tergal, and all parts 
on the ventral aspect are sternal. The genital tube, being 
ventral of the anus, can therefore contain no tergal parts ; 
though one or more sternites may enter into its composition. 
Hopkins * considers our tegmen in Pissodes as “repre- 
senting the apodeme of the ninth tergite”” Bugnion + 
considers that in Cissites testacews the median lobe (“ gout- 
tiere interne ”) is derived from the ninth segment, and the 
tegmen (“gouttiere externe”) from the tenth segment. 
* U.S. Dept. Agr. Technical Series, No. 20, Part I, 1911. 
t Bull. Soc. Ent. d’Egypte, 4"° Fascicule, 1910. 
