TIIE RAT-FLEA, CERAT0PHTLLU8 FASCIATUS BOSC. 459 



open by pressure under a cover-glass when freshly dissected out. 

 In one of my specimens the receptaculum is empty and contains 

 no spermatozoa ; this specimen is also the only one I have 

 succeeded in mounting in Canada balsam without any shrinkage 

 taking place in the hinge-region. This virgin receptaculum also 

 shows some structures in the interior, the nature of which I have 

 not been able to make out clearly, but which look rather like 

 prolongations of the duct into the interior of the main chamber. 

 Sections would be necessary, however, to determine the nature of 

 these internal arrangements, which are not visible in any of my 

 specimens that are filled with spermatozoa. 



The duct of the receptaculum (d., d., d.) is of extraordinary 

 length, and just where it arises from the main chamber it is 

 surrounded by a cushion of deeply staining, closely packed cells 

 of glandular appearance (gl.c.), each shaped somewhat like an 

 Indian club. The duct itself has an irternal chitinous lining 

 secreted by an external epithelial layer, which is shallow and 

 contains small nuclei in great number but shows no distinct 

 cell-outlines. At its proximal end, immediately after it comes 

 through the glandular cushion already mentioned, the duct is 

 surrounded by a great number of rounded cells (gl.), which have 

 clear, lightly staining contents, and present also a glandular 

 appearance. The rounded cells are thickly clustered round the 

 proximal end of the duct, but as the duct is followed along in 

 a distal direction they diminish in number and gradually thin 

 out until, about half-way along the duct, they disappear 

 altogether, and the distal half of the duct consists only of the 

 chitinous lining and the epithelium with small nuclei. 



As the duct approaches its termination it shows some peculiar 

 complications, forming what I propose to call the terminal organ 

 (T.O.). First of all there is a feeble imitation of the corkscrew- 

 organ in the shape of a broad expanded plate, apparently 

 chitinous, on one side of the duct, which performs a spiral 

 twist of one complete turn. The spiral portion passes on into 

 a short length of the duct, which has on one side a thickening 

 of the chitin to form a strong bar (c.b.), bent like a bow, which 

 is strung, so to speak, by a strong muscle of four or five fibres 

 (m.t.o.). I have not been able to determine exactly by dissection 

 where the duct finally opens, whether into the unpaired oviduct 

 or into a terminal genital vestibule or vulva ; sections, or 



