AND ZOOGEOGRAPHY OF INDIAN OLIGOCH.ETA. 127 



well-marked connective-tissue (blue-staining) coat, 2-5 ^i thick 

 and rather loose in texture. 



Having reached the parietes it runs backwards for a short 

 distance, and then, sinking into the body-wall, lies in the blue- 

 staining connective tissue between the two muscular layers ; 

 here its diameter is 30 /i, and its connective-tissue coat is still 

 moderately thick. Arrived at the base of the prostate, it enters 

 this organ at its lower end, and runs upward outside the 

 muscular coat of the prostate and within the layer of large cells, 

 in a direction parallel to the prostatic lumen ; its diameter is 

 now 20 ju, and it still possesses a deeply staining connective- 

 tissue layer outside its epithelium. Sinking through the 

 muscular layer of the prostate, the rest of its course lies within 

 that coat, in the lining epithelium (fig. 3, v. clef.) ; it finally opens 

 into the prostatic lumen at the ental extremity of the latter. 

 In this 'last part of its course it loses its blue-staining layer and 

 becomes a small, round tube of cubical cells, 18 /i in diameter. 



The actual i-elations of vas and prostate are thus disguised, 

 inasmuch- as the vas, entering the prostate at the base of the 

 latter, and ascending within its wall to the apex, is hidden from 

 view dui'ing this part of its course. In a species of Dravnda 

 {D. razri) which I have recently described (28), and which is in 

 respect of its male apparatus the most primitive of the genus (it 

 possesses two pairs of prostates, an ancestral chara.ctei-), " the vas 

 deferens, joining the prostate below, can be seen running up its 

 surface towards the free upper end." In Moniligaster deshayesi 

 the prostates are very large and sausage-shaped, and extend back 

 through several segments ; ■ the vas deferens passes back along it 

 to fuse with it some little distance from its ental end ; and 

 presumably sections would show that here, too, the vas is a 

 separate tube as far as the ental end of the prostate, where the 

 one presumabl)^ passes into the other ; in two varieties of this 

 species the vas can be seen in an ordinary dissection to enter the 

 ental end of the prostate. 



In certain species of the genus Dravnda, therefore, and more 

 obviously in the genus Moniligaster, the prostate is to be regarded 

 as the thickened continuation of the vas defei^ens surrounded' by 

 a bulky mass of peritoneal cells. These cells give the organ th6 

 soft and papillose surface which frequently characterizes it. In 

 other species of Drmoida, however, the surface of the prostates 

 is firm and shining — an appearance which is associated with a 

 firm muscular investment ; either there is here no soft covering 

 of swollen peritoneal cells, or the layer is so intermixed with and 

 covered by muscular fibres as to give a firm and resistant 

 surface. 



(5) The Ovarian Chamber and its Contents. 



The first indication that there is anything peculiar in the 

 septa which come into relation with the female organs in the 



