UROGENITAL SYSTEM OF MYXINOIDS 121 



the North-American Myxine does not present any striking 

 differences. 



The single ovary occurs on the right side, and extends from 

 the region of the gall bladder to the posterior end of the coelomic 

 cavity, and is approximately (within 2 or 3 cm.) one-half the 

 entire length of the animal. It is suspended in the body cavity 

 by a single mesovarium, which is attached along its proximal 

 margin to the mesentery where the latter joins the dorsal sur- 

 face of the alimentary canal, to the right of the supra-intestinal 

 vein. In young animals the mesovarium presents a perfectly 

 flat surface, but in specimens which have eggs 5 mm. long or 

 more it becomes folded transversely, being most folded in the 

 oldest females. The distal margin of the mesovarium does not 

 take part in this folding, but remains straight, therefore the two 

 margins are much shorter than the rest of the mesovarium, a 

 condition which causes the mesovarium to bulge out laterally. 



For about 10 mm. at the anterior and posterior ends, the 

 mesovarium is merely a hne along the dorsal surface of the 

 digestive tract, then increases more or less abruptly to its aver- 

 age width. At the posterior end it decreases more or less gradu- 

 ally to a Une on the dorsal surface of the aUmentary canal, and 

 ends at the genital pore. Even in the youngest females, where 

 the mesovarium is simply a flat sheet, its width varies at dif- 

 ferent points along its course (fig. 65). In successive older 

 stages these inequalities in width are more and more pronounced, 

 the widest points being where the eggs are attached. In the 

 youngest specimens (no. 18) the mesovarium is 2 mm. wide 

 at the widest points, and in Myxine no. 2, which has eggs 22 

 mm. long, it is as wide as 30 mm. where the large eggs are at- 

 tached. Between these large eggs the mesovarium is from 10 

 to 20 mm. wide. The weight of the eggs doubtless stretches the 

 mesovarium, for it is drawn out into an elongated strand where 

 each egg is suspended. Frequently these strands are inter- 

 twined and even tied in knots. In specimen no. 20 the meso- 

 variun is 25 to 30 mm. wide and the strands to which the corpora 

 lutea are attached extend only 3 or 4 mm. beyond the general 

 width of the mesovarium. In one of the oldest females the 



