THE REARING OF SEA-FISH LARV.E. 73 



could bridge the gap in our knowledge as to the proper methods of 

 treating the fry during the transformation from the larval to the 

 adolescent stages. Promising as are the results of the experiments 

 described above, it is clear that our knowledge of the conditions of 

 larval life and development is quite inadequate so long as we can only 

 ensure the survival of a minute percentage of the fry in our rearing 

 experiments. 



The species employed in my experiments was the " Butterfly Blenny " 

 {Blcnnius ocellaris), which, at Plymouth, usually lays its eggs in the 

 empty shells of whelks {Buccinum), in moderately deep water offshore 

 (15 to 20 fathoms), whence relays of its eggs were easily obtainable 

 with the dredge during the past summer (1899). 



Although many offshore types of fish doubtless differ from it as to 

 the special conditions requisite for their development, yet the observa- 

 tions made upon the development of this species cannot be without 

 value in regard to the rearing of other offshore larvce in captivity. 



The eggs of the Butterfly Blenny have been described by Cunning- 

 ham,* and the structure of the larva soon after hatching by Holt.f 

 The larva at this stage is already well organised : the mouth is formed, 

 the eyes pigmented, the yolk relatively small in quantity and 

 moderately protuberant, and the pectoral fins well developed. On the 

 other hand, the vertical fin membrane is still in the primitive undivided 

 condition, the lower jaw is immovable, and the permanent skeleton 

 has not yet made its appearance. The larva thus approximates in type 

 to the early larva of Cottus and other demersal forms, and is more 

 highly organised than the early larviu derived from pelagic eggs such 

 as those of fiat fishes and gadoids, which indeed do not, strictly speak- 

 ing, merit the term " larvte," since they are merely embryos released 

 from their shells, and incapable of capturing food for themselves. 

 These so-called " pelagic larvse " (which are not more peculiarly pelagic 

 than the larvse arising from demersal eggs) might well be distinguished 

 from true larvfe, as " embryonic larvie " or " embryo larva." The larva 

 of the Butterfly Blenny, at the time of hatching, corresponds in its 

 grade of organisation with a plaice larva five or six days old. 



Holt assigns a length of 6'30 mm. to the larva of the Butterfly 

 Blenny when twelve to twenty-four hours old. This dimension consider- 

 ably exceeds that of all the specimens which I have measured at a 

 corresponding age, as will be seen from the following records of the size 

 of four specimens, in millimetres : — 



* Journ. M. ^. ^., i. 1891, p. 36, fig. 35. 



t Ann. du Muse'e d'Hist. Nat. dc Marseille, ZooL, v., 1899, p. 45, pi. 6, fig. 63 ; 

 Jouni. M.B.A., V. p. 122. 



