204 THE SWIM-BLADDER OF FISHES 



all reference to its special features in the embryonic or larval 

 stages of fishes. To understand the true nature and sig-nificance 

 of any organ it is necessary to study its development, yet no 

 authority, so far as I am aware has made reference to the 

 remarkable features of the swim-bladder in the embryonic 

 stages. Few have had the opportunity to study the larval 

 development of fishes possessing this organ ; and ray own 

 researches show, as might have been expected, how in the larval 

 stages the swim-bladder reveals its primitive character, and that 

 the variations in its form, position, connections, and minute 

 structure, observed in adult fishes, are secondary, non-essential, 

 and very seriously misleading. It is, however, on these 

 secondary and misleading modifications that authorities have, 

 almost without exception, based their views as to the nature 

 and meaning of the swim-bladder in fishes. On very flimsy 

 and inadequate evidence many eminent authorities have not 

 hesitated to attribute extremely varied functions to this organ, 

 and it is certainly remarkable that the most generally adopted 

 views have the least support from observation. Young larval 

 fishes in the sea swim in a reversed position, back downwards, 

 and it might be supposed that the development of the swim- 

 bladder aided them in " righting " themselveo, and progressing 

 dorsum uppermost, as they do later in life : but those without 

 the organ adopt the latter position as readily at the accustomed 

 stage as those possessing it. If it be hydrostatic it is difficult 

 to see why fish specially needing buoj^ancy, like the surface 

 frequenting sharks, the ponderous oceanic sunfishes (Molida3), 

 often more than a ton in weight*, the huge tunny, the mackerel, 

 &c., should be destitute of it, while the shore-loving Gobiida^, 

 Scorpa3nida3, Triglidas, Gastrosteidfe, &c., have it well developed 

 and of large size. The Scia3nida3, including no fish frequenting 

 the deep waters of the open sea, have this organ in its most 

 elaborate forms. It is large in the fresh- water whitefishes 



*ThiM monstrous flsh {Mola)A^ Packard sxy.-!, (Xo. 17, p. 162), " i-; like other.-; of the 

 order, a surface switniner." 



