68 M. E. Storms on the Adhesive Disk o/Echeneis. 



1. The first, generally adopted, explains it as a modified 

 dorsal fin. Voigt, according to Dr. Giinther *, was the first 

 to give this interpretation, which was also put forth by 

 Blainville t) Agassiz |, and most writers. 



2. The second interpretation, much less known, was sug- 

 gested by Kner §. He compares the organ of Echeneis to the 

 scutes and spines of Gast7'osteus, and explains them all as 

 modified dermal ossifications. 



There can be little doubt as to the first interpretation being 

 the true one, because 



1. The disk occupies the position of a spinous dorsal fin; and 

 as Echeneis by its other characters can be proved to belong to 

 the Acanthopterygians, it is natural to think that the missing 

 spinous dorsal has served to form the disk. 



2. Some parts of the disk, i. e. the interneural spines, are 

 so little transformed that they are easily recognizable. 



3. As will be shown further on, it is not only the inter- 

 neural spines, but also the other elements composing the disk, 

 that can be compared to those which enter into the structure 

 of a normal spinous dorsal fin. 



As for the other opinion, it does not satisfy any of the 

 foregoing conditions. 



II. 



MOEPHOLOGICAL VaLUE OF THE ELEMENTS OF THE DiSK. 



If most authors agree in regarding the disk as a modified 

 dorsal fin, there is much greater uncertainty as to the inter- 

 pretation of the different bony elements which enter into its 

 composition, and also as to the way in which these have been 

 modified. 



1. Voigt II, Blainville^, and the older authors regard the 

 buckler as formed of a fin, the rays of which have been bent 

 downwards on both sides. 



2. Dr. Giinther** explains each pair of lamellae of the disk 

 as formed out of one spine, eacli half of which is bent down 

 towards the right and left. 



• A. Giinther, "On the History of Echeneis'' Ann. & Ma^. Nat. Hist 

 [3] 1860, vol. V. p. 389. 



t A. Giinther, loc. cit. I have not been able to consult the original 

 papers of Voigt and Blainville. 



\ L. Agassiz, Recherch. Poiss. Foss. vol. v. p. 117. 



§ Dr. Rudolf Kner, " Ueber den Flossenbau der Fische," Sitzuno'sb 

 kais. Akad. Wiss. Rd. xliv. 18r5l, p. 62. ^ 



II Dr. Giinther, loc. ctt. p. 389. 5[ Id. ibid. 



** Dr. Giinther, 'The Study of Fishes,' p. 460. 



