292 Bionomics of Weevils 



the genital tube is everted during copulation, the anterior end of the 

 internal sac becomes the apex of the tube, and it is on this transfer 

 apparatus that the functional orifice is situated. 



The median lobe (Fig. 5, II, III, IV and V, M.) has the under-surface 

 and sides chitinous and thus resembles a trough, the sides of which 

 decrease in size towards the apex. It is of characteristic shape in the 

 different species of Sitones which I have examined. It bears anteriorly 

 two long chitinous struts which arise from its ventral surface with a 

 pronounced angular curve. Between those struts and partly surrounding 

 them is a mass of longitudinal muscles extending from the median lobe 

 to the apex of the struts. These muscles encircle the apex of the internal 

 sac and the transfer apparatus, and to examine these structures the 

 genitalia have to be boiled in caustic soda to remove the muscles. The 

 median Jobe is protruded from the body during copulation but does not 

 enter the genital tube of the female, the internal sac being everted 

 through its apex. The median lobe measures 0-54 mm. long by 0-294 mm. 

 broad, the struts 0-77 mm. long. 



The tegmen (Fig. 5, II, T.G.), the chitinous part of the tegminal layer 

 which forms the portion of the genital tube connecting with the apex 

 of the abdomen, is represented by a semicircular band of chitin bearing 

 anteriorly a short median strut. The median lobe when not functioning 

 is drawn within the tegmen, so that the latter appears to be situated at 

 its anterior edge on the ventral surface. 



The spiculum gastrale (Fig. 5, VI) is a slightly curved chitinous rod 

 which occurs beneath the genital tube at the apex of the abdomen. It 

 is a median unpaired structure with the anterior end enlarged and the 

 posterior end expanding into a spatulate disc. It measures 0-961 mm. long. 



• Development of the Reproductive Organs of Male. 



The male of Sitones lineatus is mature nine months after emergence 

 in the spring of the year following its emergence. The immature male 

 (Fig. 5, II and II A) differs from the mature male (Fig. 5, III) in the 

 following respects. 



(1) The testes are smaller, measuring 0-8 mm. long by 0-6 mm. broad. 



(2) The seminal vesicles are smaller, measuring 0-21 mm. broad by 

 0-13 mm. long. 



(3) The seminal tubes are considerably smaller in size and breadth. 



The other parts are the same as in the the mature male. The repro- 

 ductive organs of the male weevil remain in this condition during the 

 winter but growth commences about March. 



