46o THE DOGFISH chap. 



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, and pin them down, ventral side upper- 

 most, 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. Ii8, 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, 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 may be injected), and then dissect out, on 

 one side — a, 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. Ii8, b), the thin-walled, anterior united ends 

 of the oviducts, their thick-walled posterior portion, the 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 tireters will be seen on either side. Cut open the 

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

 Sketch. 



£. Circulatory' and Bespiratory Organs, &c. 



I. — After noting the spinal nerves, exposed by the removal of the 

 kidneys, the body may be cut through first behind the pectoral arch, and 

 the posterior portion thrown away. Pin down the head and anterior 

 portion of the body, ventral side uppermost, make a median longi- 

 tudinal incision through the skin from the lower jaw to the pectoral arch, 

 and dissect it away on either side as far as the gill clefts. Then, 

 without injuring the lateral vein (p. 458), remove the middle portion of 

 the pectoral arch and expose the pericardial cavity and heart. Insert a 

 seeker, pointing backwards, along the dorsal side of the heart, through 



1 See also C- § HI- 



