NORTH SEA INVESTIGATIONS. 371 



of such a process. I have certainly met with an instance of atrophy 

 of the ovaries in another species, but it was evidently of a patho- 

 logical nature, and conducted along- lines which seemed very unlikely 

 to result in a simulation of the immature condition {vide p. 382) . 



To recapitulate, I would state that when retained ova are not 

 present to place the matter at once beyond doubt, a spent can always 

 be distinguished from an immature ovary by the wide flaccid ante- 

 rior region, by the greater length of the posterior process,* and by 

 the loose manner in which the latter is lodged in the cavity along- 

 side of the haemal spines. Indeed, if the specimen is fresh, a groove, 

 which can be felt by passing the finger along the skin in this region, 

 is almost a sufiicient test ; but if the fish is more or less stale, the 

 groove is to some extent perceptible even in immature fish. 



The members of group (&), viz. the common sole, lemon sole, and 

 witch or pole dab, present rather more difiiculty, as there is never 

 any great dilatation of the anterior part of the ovary, and its pos- 

 terior process is more or less elongated from a rather early period. 

 In soles of three or four inches, and in lemon soles of six inches (the 

 smallest I have been able to procure), it is already considerably 

 developed. Moreover in all forms the backward extension of the 

 gut on the ocular side prevents any constriction of the corresponding 

 ovary by the caudal muscles ; and in the case of the sole the same 

 effect is attained on the blind side by the disposition of the hind part 

 of the kidney and the urocyst. In the lemon sole and pole dab 

 the ovary is the only occupant of the cavity on the blind side of the 

 hgemal spines ; yet in the former it is but little occluded by connective 

 tissue in the posterior region at any period, whilst even the anterior 

 part, which is so firmly fixed by the caudal muscles in immature 

 members of group (a), is always comparatively loose. I have not been 

 able to examine enough small pole dabs to know whether the same 

 holds good for that species also, but I believe it is the case. 



A recently spent ovary can, of course, be easily detected as such 

 by the nature of the germinal epithelium, and usually by the presence 

 of retained ripe ova. Thus in the sole the degenerating follicles, 

 deeply coloured by haemoglobin, are very conspicuous, much more so 

 than in any other species I have studied. Again, ova which have 

 passed the inactive condition have been present in all spent ovaries 

 which I have examined, and entirely absent from specimens I have 

 considered to be immature. The ovary itself is also longer and 

 wider, and flaccid anteriorly in the former condition, and narrow, 

 plump, and rounded in the latter, but more conspicuously so in the 

 sole than in the lemon sole. The length is a matter of comparison ; 

 thus in the sole I have not found immature ovaries to exceed two 



* This is, of course, a matter of comparison, accordiug to the species. 



