THE RAT-FLEA, CERATOPHYLLUS FASCIATUS BOSC. 453 



other, and then the duct of the testis lying more anteriorly runs 

 straight back, while that of the testis situated more posteriorly is 

 coiled. When the testes are smaller, as in the older, more 

 exhausted males, they lie side by side and their ducts run straight 

 back. 



When the testis is examined it is seen at once to consist of two 

 parts, a dilated bladder-like portion of ovoid shape, at the base of 

 which is a coiled tubular portion. The bladder-like portion 

 appears to be the testis proper (T ), while the coiled tubular 

 portion (ep. 1 ) recalls the structure in the human testis known as 

 the epididymis, and may be known conveniently by this designa- 

 tion. In one of my dissections I succeeded in uncoiling the 

 epididymis forcibly, by pulling on the duct (ep. 2 ). It was then 

 seen that the epididymis is a thin-walled tube, tilled with ripe 

 spermatozoa ; consequently, from the point of view of function, 

 the epididymis represents a vesicula seminalis, that is to say a 

 receptacle for the storage of ripe sperm.* 



The calibre of the tubular epididymis narrows rapidly as it 

 passes on into the duct, which may be called here, as in other 

 animals, the vas deferens. The right and left vasa deferentia (v.d. 1 , 

 v.d. 2 ) run back a little way and join to form the common vas 

 deferens (v.d. 3 ), but it can be seen very easily that the union of 

 the paired vasa deferentia is merely external and not internal, 

 since the lumina, or internal cavities, of the two ducts remain 

 quite distinct. 



The common vas deferens runs to a set of glandular structures 

 which I regard as corresponding to a prostate gland, and consist- 

 ing altogether of four blind tubular diverticula ; a median pair of 

 short tubules, which maybe termed the median prostates (r.m.p.), 

 and a much longer pair of lateral tubules, which may be called 

 the lateral prostates (r.l.p.). The two median prostates are in 

 close contact, but their cavities are quite distinct and independent. 

 The walls of the tubules are composed of a single layer of 

 glandular epithelial cells of small size, which show in surface view 

 very distinct polygonal outlines (PI. 30, B). The tubules contain 



* The structure of the testis was not quite correctly described in our 

 monograph on the development of T. leicisi (Minchin and Thomson, I.e.). 

 When that was written I had not seen the epididymis uncoiled, and 

 regarded the dilated bladder-like portion of the testis as a vesicula 

 seminalis. 



