of the Fisher// Board for Scotland. 



339 



anomalous. An examination of the skull shows that the distortion of 

 the bones caused by the migration of the eye is quite as complete as in 

 the other forms, yet the parts in connection with the lower nasal organ 

 display no trace of this. Externally we see that the organ of the blind 

 side is in its normal position (Fig. 4. l.n.o.), i.e. in a similar position to 

 that of the eye side. It lies a little distance from the extremity of the 

 snout above the maxillary portion of the mouth. This position of the 

 nasal organ of the blind side — which is practically the same in all the 

 species of Soleida? examined — gives rise to a problem somewhat difficult 

 of solution when we consider that the Soles are descended from one or 

 perhaps two of the preceding groups. If the nasal organ of the blind 

 side in those groups has been carried upward towards the ridge of the 

 head, how has it come about that it remains in its original position in the 

 Soleidae ? The position of the dorsal fin does not afford an explanation, 

 because the development of the fin forwards in the earlier stages of the 

 species whose development is known is just the same as in the Turbot- 

 group. It may be that this organ begins to function very early, and 

 that the underlying structures become disconnected from the parts 

 which are affected by the migration of the eye. This is a problem, how- 

 ever, which can only be solved by a comparative study of the changes 

 in structures that take place during the migration of the eye. 



It has thus been shown that the position of the nasal organ of the 

 under or blind side differs in the five groups mentioned. It is probable 

 also that these respective positions will be the same for the species that 

 still remain to be examined. 



The position of the nasal organ of the blind side would thus appear 

 to be a character of more than generic importance. In the first four 

 groups its position depends upon the relation between the anterior 

 extremity of the dorsal fin and the migrating eye. The utility of this 

 organ is nevertheless probably equal in all, because the actual position 

 on the head is not very different. And we thus have an example of an 

 important difference arising in one character independently of utility 

 on account of relative alterations in other characters. In the case of 

 the Soleida? the position of the organ in question is probably connected 

 with its utility. This character is, however, of minor importance in 

 comparison with differences in the internal structure of the nasal organ 

 to be now described. These differences have been already noted by 

 Bateson (6), but as he examined only a few species, it apparently did 

 not occur to him that they were of great importance. 



In the Halibut- and Plaice-groups it is found that the olfactory 

 lamina? run parallel to the main axis of the body. The sensory 

 epithelium is simple and comparatively slightly developed, the lamina? 

 being but little raised from the level of the basal supporting membrane 

 (Fig. 5, o.o.). In the Citharus- and Turbot- groups the epithelium is 

 more developed and complex. The lamina? are arranged in the form of 

 a rosette about a median rachis which runs parallel to the main axis of 

 the body. The lamina? are therefore disposed transversely to this axis. 

 In the Sole- group the olfactory organ is similar to that of the Turbot- 

 group, but is not so distinctly rosette-shaped. The lamina? are arranged 

 about a median rachis, but in the form of a leaf in many cases 

 (Fig. 6, o.o.) ; in other cases the rachis extends the whole length of the 

 underlying membrane, and the lamina? are arranged bilaterally along- 

 each side. In the genus Solea (Fig. 7) the rachis of the sensory 

 epithelium lies transversely to the main axis of the body, but in other 

 genera ( e.g. Cynoglossm ) the rachis is placed longitudinally, or slightly 

 inclined to the longitudinal axis of the body. In the groups from the 

 Australasian fauna, Ehombosolea, etc., and Brachyplewxc, the olfactory 



