14 



ZOOTOMY. 



the testis is a soft, greatly lobulated organ, closely resembling 

 fat : the ovary (Fig. 4, oii), is also multilobular, each lobe 

 containing numerous eggs, each about the size of a pin's head. 

 The genital gland is suspended to the dorsal wall of the 

 abdomen by a sheet of peritoneum, called mesorchium in 

 the case of the male, mesoarium in that of the female. 

 In the breeding season, the body cavity is found to be quite 

 full of liberated ova, and the ovary itself is much reduced. 



Fig. 7.— Petromyzon marinus. Transverse section through the 

 abdominal region, including the first dorsal fin (nat. size). 



cd, cardinal veins: d.ao, dorsal aorta: f.r, fin rays: f.t, fibrous 

 tissue inclosing neural canal : int, intestine, the line pointing to the 

 spiral valve : k, kidneys : ly, sub-vertebral lymph sinus : m, body- 

 muscles : my, myelon : nc, notochord : n.ca, neural canal : ts, testis : 

 ur, ureter. 



39. The intestine (Figs. 4 and 7, int), a straight, very 

 slender tube, entering the body-cavity at its anterior end 

 and on the dorsal side : it passes backvi^ards between the 

 liver and the genital gland, and then between the lobes of 

 the latter, till it reaches the posterior end of the body-cavity, 

 where it dilates into the rectum (Fig. 5, r), and ends by 



