440 Survey of Fishing- Grounds, West Coast of Ireland, 1890-1891. 



from a hypothetical ancestral form in which the median fins were entirely con- 

 tinuous round a diphycereal caudal extremity need hardly be suggested ; while 

 such a condition is apparent to this day within the limits of the Gadoid group in 

 such forms as Fierasfer and Oj^hidion. The latter, however, can hardly be cited 

 as retaining the ancestral condition, since our knowledge of their phylogeny leaves 

 it uncertain that their present conformation (especially in the case of the parasitic 

 Fierasfer) may not rather be indicative of a degeneration from a degree of 

 specialization, conforming more nearly to that exhibited by the higher members of 

 the grou^J. There is, perhaps, less occasion for such speculation in the case of the 

 Lycodidse, and, in any case, all our knowledge of the evolution of the Ichthyojjsida 

 points so distinctly to the derivation of the present divided and median fins from 

 an originally continuous organ, that the matter need not be further dwelt upon. 



In Brosmius (fig. A) it will be noted that the dorsal and anal fin rays are not 

 of equal height throughout, those in the central parts oj these fins being so far 

 reduced as to impart a slight incurvation to their outlines, a phenomenon which 

 may be recognised as the inception of a sub-division of the single dorsal and 



Fio. A. 



anal into more numerous elements. The condition of Molva, Merluccius, Phycis, 

 IIaloporj)liyrns,* &c., may either come next in the series, or may possibly be 

 parallel to that of Brosmius. The former have a short, separate first dorsal and a 

 long second dorsal, which, like the anal, show an incurvation of the outline, 

 practically identical in position with that which we have noted in Brosmius. 

 We are acquainted with no form in which the separation of the first dorsal (of 

 Merluccius) is foreshadowed by a reduction in the length of the rays comparable to 

 that apparent in the posterior part of the whole fin, but in such a form as Banicej)s 

 we have perhaps a stage in the degeneration of a short separate first dorsal, and in 

 Motella of its specialization to subserve a function in no way connected with 

 natation, t It is possible, therefore, that the present condition of the dorsal in 

 Brosmius may have been arrived at by the consummation of such a process of 

 degeneration of a separate first dorsal as appears to be exemplified by Eaniceps, 



* 



Cf. figs. 1 and 2, PL xxxix. 

 f Wc alludu to the peculiar ciliary function of this fin, but arc unable to offer any interpretation of its 

 value. 



