132 Mr. D. M, Paul on the Pelvic Fins in the 



XVI. — On the Pelvic Fins in the Postlarval and Yovng Stages 

 of Onus mustela [the Five-hearded Rockling). By David 

 il. Paul, Gatty Marine Laboratory, St. Andrews. 



[Plate v.] 



The young of this form lias at different times and by different 

 observers been described as a distinct species, principally on 

 account of the great development of the pelvic fins and the 

 difference in coloration from the adult. The young fi.sh was 

 first described by Couch* under the name of '^Ciliata 

 glauca^^'' the generic name being given on account of the 

 peculiar character of the first dorsal fin. The name " Ciliata,^^ 

 however, was already occupied, and Thompson f proposed 

 the name "Couchia,^^ and this was the term used by Glinther 

 in his ' Catalogue of Fishes in the British Museum ' |. It 

 was pointed out by Malm, and. soon afterwards by Liitken §, 

 that this was not a distinct species, but merely the young 

 stage of the rockling. In popular language the young fishes 

 are knfjAvn as the " mackerel midges," because they afford 

 food to large numbers of mackerel and other fishes which follow 

 and prey upon them as they swim in shoals. A similar, if not 

 identical, form was described by Agassiz ||, and its early 

 development studied by him and Whitman^. The early 

 development has been studied in this country by Brook **, 

 ■who also gives a short note on the postlarval stages of the 

 allied species 0. cimhria. In this paper he gives a table 

 showing the sizes of the fish and of its fins at different stages. 

 The postlarval and young stages were also described by 

 M'Intosh ft and Prince :j::j:, and the former has also a paper §§ 

 in which he studies in greater detail the later stages in the 

 growth of this species. In all these papers, however, the 

 later development of the pelvic fins has only been touched 

 upon, and more attention has been paid to the changes in size 

 and external appearance than to the structure and function of 

 these fins at different stages in the life-history of the fisli. 



* Loudon's Mag. Nat. Hist. vol. v. pp. 15 & 741. 

 t Nat. Hist. Ireland, vol. iv. p. 190. 



I Vol. iv. p. 363. 



§ Smitt, ' iScandiuavian Fishes,' pt. i. p. 544. 



II I'roc. Amer. Acad. Sci. & Art, vol. xvii. (1882). 

 T Ihul vol. XX. (1884). 



** Linn. Soc. Joum., Zool. xviii. 

 tt Proc. Pioy. Physical Soc. Edinb. vol. x. 

 Jt Trans. Rov. Soc. Edinb. xxxv. p. 832. 

 §§ Scot. Pish. Board Hep. 1896, p. 203. 



