THE RAT- FLEA, CERATOPHYLLVS FASCIA TVS BOSC. 457 



the body than the point of insertion of these bars (b 2 ). I think 

 it probable that there are more muscles attached to b 2 than 

 are seen in my figure, but have become torn away in the dis- 

 section. Both b 1 and b 2 can be seen clearly through the body- 

 wall in the uninjured flea. From the thick beam of chitin 

 which forms the dorsal part of the penis a lateral muscle (l.m.) 

 omes off, which is probably attached distally to the integument. 



In one of my preparations treated with potash, spermatozoa* 

 could be seen very plainly in the interior of the urethral duct, 

 and they have been put into the figure on PI. 29 in order to 

 show the course of the duct. The spermatozoa (sp.z.) begin in the 

 lowest coil of the corkscrew -organ, where they show a peculiar 

 festoon-like arrangement. As the duct passes into the body of 

 the penis, the spermatozoa take on an arrangement in wavy 

 bundles and the calibre of the duct widens considerably, and 

 at the same time the spermatozoa show that the duct crosses over 

 the chitinous bar which forms the inner boundary of the duct in 

 the corkscrew-organ, and which has now become very much 

 thinner and more delicate, passing on to be merged into a much 

 thicker bar on the ventral side of the penis. Just a little 

 in front of the middle region of the penis the spermatozoa are 

 heaped up in a way that shows the duct to have become greatly 

 enlarged in calibre, but behind this point the spermatozoa dis- 

 appear altogether. In stained preparations it can be seen that 

 the penis has a superficial layer of muscles which appear to have 

 a criss-cross arrangement, and lie on the wall of the widened 

 spermatic duct, but they have not been put into the drawing, as 

 their exact position and arrangement are difficult to make out 

 clearly. The contraction of the superficial muscles would doubt- 

 less have the effect of contracting the lumen of the penis and 

 ejecting the sperm. 



Such are the main points of the structure of this very com- 

 licated apparatus, so far as I have been able to make them out ; 

 but I think it probable that there are more minutiae to be 

 described, especially with regard to the structural details of the 

 penis and " corkscrew-organ." 



IV. The Female Reproductive System. 



As regards the primary sexual organs of the female sex, they 

 are of the usual insectan type, and can be dealt with briefly. 

 Journ. Q. M. C, Series II. No 76. 32 



