522 PHILOSOPHICAL TRANSACTIONS. [aNNO I789. 



careless manner ; there are others however which are truly worthy of their au- 

 thor, and in which the specific characters are pointed out with that clearness and 

 precision, which so eminently distinguish the descriptions of Linnaeus from 

 those of all his predecessors. 



In the construction of the class, Linnaeus has been particularly unfortunate ; 

 as he has erred, not only in making a unilocular heart one of the characters of 

 it, but also in making the cartilaginous fishes a part of it. Every anatomist now 

 agrees that the Amphibia Nantes are not furnished with lungs ; and every natu- 

 ralist is convinced of the propriety of removing them from the class of amphibia, 

 to that of fishes. By the removal, the name of the class becomes much less 

 objectionable ; there being few genera, in the 2 orders of which it is now pre- 

 sumed to consist, which do not contain animals to which the term amphibious 

 may, with some propriety, be given ; whereas, in the order of Nantes, not one 

 species occurs which has the smallest claim to that title. With respect to the 

 other error, viz. that of supposing the hearts of the amphibia to be single, it 

 would be easy to show that it was not an uncommon one, at the time Linnaeus 

 formed his system. And indeed it appears he was led into it, by following an 

 author whom he probably supposed of too great fame not to be safely relied on. 

 At least, in defence of his opinion, he quotes the following words of Boerhaave. 

 " In omnibus animalibus in quibus sanguis non calet, ventriculus cordis est 

 unicus." It is sufficient for the purpose to observe, that the hearts of most of 

 the amphibia are now well known to be double, with an immediate communica- 

 tion between the 2 cavities ; which structure seems peculiarly adapted to that 

 change of element, which many of them can for a time support ; and thereby 

 furnishes another argument in favour of the name Linnaeus has given to the 

 class. To consider the structure of the heart however is not absolutely neces- 

 sary in forming the characters of the class : the animals of which it consists 

 being sufficiently distinguished from all others, by having cold red blood, and 

 breathing by means of lungs. These 2 characters render the class perfectly dis- 

 tinct from the rest ; the 2 superior ones, viz. mammalia and birds, having warm 

 blood; and the 3 inferior ones, fishes, insects, and worms, not being furnished 

 with lungs. 



In his generic characters, Linnaeus has been more successful than'in those of 

 the class. Whoever will be at the pains of comparing Linnaeus's genera of am- 

 phibia with those of Gronovius, will find, that the generic characters of the 

 former, though few in number, are precise and distinct ; while those of the 

 latter, though more numerous, are vague, indistinct, and sometimes inaccurate. 

 But though Linnaeus's genera of amphibia are generally well-formed, it must be 

 allowed to be a great imperfection in them, that the venomous serpents are not 

 separated from the others. From some expressions in the Preface to the Mu- 



