in the Neighbourhood of Edinburgh. 199 



the body, form an impenetrable cuirass against the teeth of other 

 inhabitants of the water, and even against the ball of a musket, 

 which makes no impression." — See the article Lepisosteus (by M. 

 Cloquet) in the Dictionnaire des Sciences Naturelles. 



But I have now to communicate a most important addition 

 to our knowledge relative to this sauroid fish, by which it is even 

 still more closely approximated to animals of a reptilian charac- 

 ter. 



The cellular structure of the swimming bladder of the Lepi- 

 dosteus had been long since remarked as curious, but it has 

 been left to M. Agassiz to discover the use of this internal struc- 

 ture, and, along with it, that of the swimming bladder itself, — 

 as this organ is usually named. Having been recently, by the 

 British Museum, allowed the permission of dissecting a specimen 

 of the Lepidosteus, preserved in spirits of wine, he has been so 

 very kind as to favour me with the result of this most important 

 anatomical investigation. 



" You know," he observes, " that the nature of the swimming 

 bladder of the fish is still an object of controversy among anato- 

 mists ; some considering it as a particular organ peculiar to the 

 class of fish, while others (the natural philosophers) suppose that 

 it is analogous to the lungs. In examining this organ, as it is 

 met with in the Lepidosteus, I have not only been enabled to de- 

 monstrate that it is a real lung, but I have also found a great ap- 

 proach in its structure to that of the lungs of reptiles. The lung 

 (the swimming bladder) of the Lepidosteus, is not only cellular, . 

 as we find it to be in salamanders, and in the reptiles improperly 

 named doubtful reptiles, but it also possesses a trachea (trachee 

 artere), which is extended the whole length of its anterior sur- 

 face, and which opens at the bottom of the mouth by a glottis 

 surrounded by ligaments which close and shut it ; — this apparatus 

 being even more complicated than we find it to be in many rep- 

 tiles. 



