686 



MR. B. F. CUMMINGS ON LICE 



sac are thicker, the cells being of varjdng lengths and their enrls 

 projecting irregularly into the lumen. The walls of the flask- 

 shaped reservoir are very thin, consisting of a clear hyaline 

 external membrane and an inner epithelium of short cells. The 

 walls of the upper portion of the ductus ejaculaiorius are very 

 thick, consisting of extremely high cells, the shape of which is not 

 clear in the prepaiations on account of unsatisfactory fixation. 

 For the same reason the histology of other parts remains obscure. 



Text-fieni'e oO. 



DV. M 



LipewmsforJic-iiJatvs. (J. Transverse section ibronjih tl'e abflomen, behind 

 the middle-sac of the vesicula. (Diagrammatic.) 



JR. rectum. D. dnctus. Bes. reservoir (lower end). DV.M. dorso-ventral 

 muscles. FC. fat-cells. 



3Iale Cppulaton/ Apparatus (text-fig. 28). — The copulatory 

 apparatus belongs to the simple type, consisting of basal plate 

 and parameres and an extrusible membranous sac (see Part I., 

 p. 257). Fortunately in the collection were two males with the 

 sac extruded, and, as usual, when in this condition turned 

 upwards and backwards over the terminal segments of the abdo- 

 men. A detailed account is therefore included of the sac when 

 extruded and when retracted, with some remarks upon the 

 mechanism of extrusion and retraction. 



The basal plate is rather long and narrow, of a dull grey 

 colour, the lateral margins a little concave. The parameres at 

 their distal ends are fused with one another. The text-figure 

 shows that the fused parameres are dorsal to the sac which shoots 

 outwards and upwards from under the chitinous arch formed by 

 the parameres. The sac proximally possesses two characteristic 

 transverse rolls caused by two deep furrows. Distally it is 

 studded with a number of minute denticles and its opening is 



