12 Fishery Board for Scotland. 



Six Rays in the First Dorsal Fin, the First Ray still small but appearing 



ABOVE THE CoNTOUR OF THE HeAD ; SECOND DORSAL AND AnAL FiNS COM- 

 PLETE. 



[Fig. 8). 



In this post-larval form, there is not a great increase in size, but the 

 development of the fins has progressed sufficiently to give some idea of the com- 

 plete pelagic form. The pectoral and pelvic fins are large ; still, there are no signs 

 of filamentous prolongations of the raj^s of the pectorals. N either are there filaments 

 to the pelvic fins, although this may he due to the difficulty in obtaining perfect 

 specimens. The pelvic fins are extraordinary, however, for the principal rays ex- 

 tend as far back as the caudal fin, and there is an enormous surface when the fins 

 are expanded. 



Another characteristic of these older post-larval forms is the persistence of the 

 embryonic fin which still remains broad. The completed second dorsal and anal 

 fins add three diameters to the depth of the tail. Even the first dorsal fin helps 

 to give depth to the fish, for the membranous sheath enveloping the bases of the 

 four posterior rays is over three-fourths of the depth of the body. The first two 

 rays of the first dorsal are not included in this membranous sheath. The first 

 ray is very small, immediately anterior to the second ray, and the tip appears quite 

 distinctly above the contour of the head. The second ray is inserted on the head 

 in front of the middle of the eye. It is relatively further forward than at the 

 previous stage. It is still very long, and ends in a filamentous tip. The third ray, 

 which is about the same length as the second, arises from the head just posterior 

 to the eye. TJie bases of the three posterior rays are v^y close to each other, 

 and arise far back on the head above the insertion of the pectoral fin. There is, 

 therefore, a greater distance between the third and fourth rays than between the 

 •second and third. 



The ravs of the caudal fin are now distinctly formed, and extend from the 

 ventral surface of the notochord to the margin of the embryonic fin. The noto- 

 chord is still straight at the tip, and is distinct from the rays of the caudal fin. 



The body has not gained much in breadth ; it has not changed greatly in form. 

 The pectorals are, therefore, still inserted high up on the side of the body, and the 

 gill-cover with the branchiostegal membrane is also distinct, when the fish is viewed 

 in profile. The mouth is large and well-developed, and the lower jaw very pro- 

 minent. The eyes are large, tending to look forwards, as well as outwards. The 

 distance from the anterior head contour to the anterior edge of the eye is slightly 

 less than the horizontal diameter of the eye. 



Stiasny (1911) has given most complete descriptions of the post-larval forms 

 after the absorption of the yolk. There is a number of points of difierence between 

 the North Sea specimens and those of the same size from the Adriatic series. 



The smallest specimen described by Stiasny is one of 10 mm. in length, but, 

 as it had remained a long tiine in formalin, its original length may probably have 

 been about 11 mm. The stage of development is indicated by the degree of devel- 

 opment of the rays of the first dorsal fin. The first ray of the first dorsal fin, 

 which later carries the two-lobed appendage, is small, almost rudimentary, and 

 sunk in a small groove above the eyes. Directly behind this, there project the 

 strongly- developed second and third rays of the first dorsal, which, with the three 

 posterior rays, are still connected by a border which is confined to the base. The 

 continuous embryonic fin connects these latter with the easily distinguished second 

 dorsal fin, in which nine rays may be counted. 



Scottish specimens of a similar length are not so far advanced in development 

 as Mediterranean specimens. At this size, the post-larval forms show only three 

 well-develo])ed first dorsal rays, and the beginnings v/ithin the embryonic fin-fold 

 of the elements of the second dorsal and anal fins in which, hov/ever, the separate 

 elements cannot be distinguished. 



Similarly, at the later stages, the Scottish specimens are larger than Mediter- 



. ranean ones at the same stage of development. The same feature has been observed 



in other species, for Petersen points out that specimens of Drepanopsetta from 



Iceland are much larger than specimens from the North Sea at a similar stage of 



