476 THE DOGFISH CHAP. 



as you do so the dorsal aorta and its various branches, and once again 

 the cardinal veins (C, III, 4), which may be inflated with air. The 

 renal portal veins are not easily traced without injection : this may be 

 done from the cut end of the caudal vein. 

 Note 



1. The brownish kidney T, and in the male the whitish forward 

 continuation of each into the anterior sexual part or epididymis. 



2. In the male : a, the convoluted spermidnct, indistinguishable from 

 the epididymis anteriorly and enlarging posteriorly to form the elongated 

 seminal vesicle; and 3, the grooved, eversible claspers, which are 

 supported by cartilages and have each a gland at the base of the 

 groove. 



II. Cut through the skin round the vent, and dissect the 

 entire cloaca and the kidneys (together with the epididymes in the 

 male) away from the body, noting as you do so some small paired 

 and median bodies in close relation to the dorsal aspect of the kidneys ; 

 these are respectively the supra-renal and inter-renal bodies (p. 447). 

 Pin your dissection down, ventral side uppermost, under water. Clear 

 away with great care the connective-tissue which binds the ureters and 

 generative ducts to the kidneys posteriorly, slit open the cloaca, and 

 make out 



1. In the male (Fig. 127, A) the aperture of the rectum , and the 

 urinogenital papilla. Insert the small scissors into the aperture at the 

 apex of the latter, and slit open the urinogenital sinus t continuing the 

 cut into the two sperm-sacs ; make out the apertures of the seminal 

 vesicles and ureters. Pass a seeker or probe into each of these 

 apertures ^(the main ureter maybe injected), and then dissect out, on 

 one side #, the elongated and pointed, thin- walled sperm-sac ; and b, the 

 delicate ureters, three or four of which unite to form a widish common 

 tube, situated towards the inner border of the kidney, before opening 

 into the urinogenital sinus. Sketch. 



2. In the female (Fig. 127,8), the. thin-walled, anterior united ends 

 of the oviducts, their thick-walled posterior portion, \\\e shell-glands, the 

 apertures of the rectum and oviducts into the cloaca, and the urinary 

 papilla. Insert the point of the scissors into the aperture on the apex 

 of the latter, and slit open the urinary sinus, in which several 

 openings of the ureters will be seen on either side. Cut open the 

 oviducts, and note, if present, the eggs enclosed in horny egg-cases. 

 Sketch. 



