334 SUPPLEMENT ON 



scomber, colias, and cordylla, and which were comprised 

 under the generic name of lacertus. There is every reason to 

 believe that these were the common mackerel and its ap- 

 proximating species. All that is said of them proves that 

 they were common and of small size. Colias lacertorum 

 minimi, says Pliny. Lacertus was, therefore, evidently a 

 name common to many species. 



One of the most curious facts in ichthyology, and the most 

 inexplicable in comparative anatomy, is, that in fishes of the 

 same genus, and so similar in all the details of their organiza- 

 tion, that very great attention is necessary to distinguish their 

 species, some possess a natatory bladder, and even a tolerably 

 large one, while others are destitute of it. What necessity 

 of nature can require this organ in one and not in the others? 

 What cause can have produced it ? These are indubitably 

 very great problems, either in the study of final causes, or in 

 the philosophy of nature in general. 



This fact, which is observable in more than one genus of 

 this family, has been discovered in that of the mackerel by 

 M. de Laroche. 



This interesting observation was made by this gentleman in 

 a voyage to Ivica in 1808, which he undertook in company 

 with M. Biot, and by which ichthyology has derived much 

 advantage. He brought back to the Museum of Natural 

 History some specimens of these mackerel destitute of the 

 swimming bladder, and at the same time some of the common 

 mackerel, taken in the same latitudes, and he described the 

 fact in a memoir on the fishes which he had collected in that 

 voyage. 



An individual of the first of these species {scomber pneuma- 

 tophorus), placed by the side of a common mackerel of the 

 same size, excites astonishment by the resemblance of its 

 form, and the proportion of all its parts. But when it is re- 



