THE ANATOMY OF ONCHOLATMUS VULGARIS, BAST. 121 



animal. As to tlie nature of the granules there is no clear 

 evidence. If they represented digested food in the process 

 of absorption, a more uniform distribution should occur. 

 They are probably either a digestive secretion produced in 

 cells which, although specialised, show no other signs of 

 specialisation, or excretory. There is no sign of a basement 

 membrane external to the epithelium. 



The contents are very meagre, apparently portions of small 

 Algae, but one fact is very striking — viz. the presence in 

 the adult female of large masses of spermatozoa, which have 

 found their way in through the gonenteric canals. 



The rectum is a short tube leading from the intestine to the 

 anal canal or cloaca. Its width, including walls, is 0"016 mm. 

 The wall has an outer layer of circular muscle-fibre and an 

 internal epithelium, while ganglion-cells which have gi'own in 

 from the longitudinal lines are to be found on the dorsal 

 surface. It terminates abruptly on joining the cloaca or anal 

 canal. The former I shall describe with the male repro- 

 ductive organs ; the latter is a very shoit invagination of 

 epidermis with cuticle, in the dorsal wall of whicli the anal 

 ganglion lies. 



Male Reproductive Organs. 



The male reproductive organs (text-fig. 1) consist of two 

 testes {at., pt.), an anterior and a posterior, lying in two 

 cavities, the testicular regions of the reproductive tubes 

 {ato\, iJtr.). The testicular regions open into a single ductus 

 ejaculatorius {de.), which unites with the rectum to form 

 the cloaca {cl.). The anterior testicular region runs in a 

 straight line backward into the ductus ; the posterior, on the 

 other hand, lies along the side of this structure, and it is 

 at its anterior extremity that it opens into it. 



The symmetry, it may be assumed, was originally bilateral, 

 the reproductive tract consisting of a pair of cavities with a 

 common duct, and that, as the result of the narrow form of 

 the body, one of the cavities has been turned through an angle 



