368 NORTH SEA INVESTIGATIONS. 



subequal in size, and markedly dilated dorso-ventrally in their 

 anterior region. The kidney is situated in the roof of the peritoneal 

 cavity, in front of the great haemal spine, and the urocyst between 

 the anterior ends of the ovaries and their ducts. 



[b] including the lemon sole, the witch or pole dab, the common 

 sole (and probably other members of the genus Solea). 



In these a loop of the ileum passes back on the ocular* side of 

 the hasmal spines for a greater or less distance (greatest in the solo, 

 least in the witch). The ocular is consequently much smallei', 

 having less space at its disposal, than the blind ovary, and neither 

 is very markedly dorso-ventrally dilated in its anterior region. The 

 excretory organs are as in group (a) in the lemon sole and witch, 

 but in the true sole the urocyst and the hinder part of the kidney 

 pass back on the blind side of the anterior hsemal spines. 



In immature fish of group {a) on removing the body-walls of the 

 abdominal region on either side the free anterior portions of the 

 ovary are seen to form, with the bony buttress, the hind wall of 

 such part of the body-cavity as lodges the alimentary viscera. The 

 one ovary is a little in front, the other a little behind the buttress, 

 or both may be to some extent united in front of it. They appear 

 as plump cushion -like structures, following the course of the buttress, 

 rounded off near its origin, and tapeinng into the ovary ducts 

 towards its distal extreme. Passing the finger backwards along the 

 external surface of the fish no groove is perceptible, in fresh speci- 

 mens, between the region of the vertebral column and that of the 

 interhaemal bones. Dissecting away the anterior muscles of the 

 caudal region, we find that each ovary is continued backwards for a 

 short distance alongside of the hgemal spines in a tapering process 

 terminating in a moderately fine point. 



The length of the posterior process, as compared with the distance 

 between the first haemal spine and the caudal peduncle, varies with 

 the species and with the size of the individual, but probably in no 

 case exceeds one third, and is usually much less. The whole 

 structure is very plump and firm, and is firmly embedded between 

 the heemal arches and the caudal muscles. If a seeker is pushed 

 backwards in the direction of the posterior process a considerable 

 amount of closely set connective tissue will be ruptured in its progress. 



On cutting into the ovary its lumen is found to be entirely or 

 nearly occluded by germinal epithelium, beset with inactive ova of 

 various degrees of minuteness. 



* The terms "ocular" aud "blind" are used in this paper, since they are intelligible in 

 connection with Pleuronectids, and, while eliminating the confusion between right and left 

 in dealing with a mixture of dextral and sinistral forms, do not, as it were, outrage mor- 

 phology like Fulton's qualified use of "dorsal" and "ventral," 



