THE SKATE. 59 



blowpipe passed into it, and taking care not to go too far. 

 The papilla will be found to lead into 



124. The urinogenital sinus (Fig. 18, ug.s), a small cavity attached 

 to the dorsal wall of the cloaca, into which it opens by the urinogenital 

 papilla : at its anterior extremity will be seen two pairs of apertures, 

 one pair (s.s') ventrally situated, round, and opening into the sperm 

 sacs, the other pair (ur 1 } dorsally situated with regard to the first, 

 partly hidden by the projection into the sinus of the sperm sacs, of a 

 somewhat crescentic form, and leading into the ureters ( 128). 



XXVII. Remove all that is left of the rectum, and of that part of 

 the cloaca anterior to the urinogenital sinus : slit open the 

 sperm sacs along their ventral wall ; note 



125. The greenish epithelium lining the sperm sacs, and the greenish 

 viscid fluid which fills them, and which consists of semen mixed with 

 the secretion of the sacs. 



126. A crescentic, thick-lipped aperture (Fig. 18, v.s 1 ), on the dorsal 

 wall of each sperm sac, just within (anterior to) the opening of the sac 

 into the urinogenital sinus : this aperture leads into the vas deferens. 



XXVIII. Open the lower part of the vas deferens and note 



127. Its expansion posteriorly into a chamber a sort of vesicula 

 seminalis (Fig. 18, v.s), which has its walls produced into laminae, 

 dividing its cavity into a number of compartments ; at its posterior end 

 this dilatation of the vas deferens opens into the sperm sac by the 

 crescentic aperture already noticed. 



XXIX. Carefully dissect one or both of the vasa 

 deferentia from the surrounding parts, and either 

 remove it entirely or turn it over to one side. 

 Make out 



128. The ureter (metanephric duct, Fig. 18, ur\ a. 

 delicate, colourless tube, situated close to the inner edge of 

 each kidney ; it is made up by lesser tubes proceeding from 

 the several lobes of the kidney, and passes backwards to 

 open into the urinogenital sinus by the slit-like aperture 

 already noticed. 



129. The inter-renal (Fig. 18, /.;-), a long, irregular 

 body of a yellow colour, lying just to the inner side of the 

 ureter. 



