220 PEOF. J. B. OEEENE ON THE MUTUAL EELATIOKS 



tiou of important changes in our present systems : — one, that the 

 Amj)hibians do not form a natural class, distinct from the E^eptiles 

 proper; the other, that between Fishes and Amphibians there 

 exists no definite line of separation. On each of these heads it is 

 proposed to offer a few brief remarks. And first, as to the rela- 

 tionship between Amphibians and Eeptiles. 



Most zoologists will probably admit that the characters which 

 seem to separate Fishes from Amphibians are of a far less funda- 

 mental nature, though apparently more striking, than those which 

 distinguish the latter from Reptiles rightly so-called. Fishes and 

 Amphibians agree in certain well-known featiu-es, wherein they 

 differ from all other Vertebrates. Both possess gills, which some 

 Amphibians and all Fishes retain during the entire period of their 

 lives. Both, moreover, are equally destitute of amnion and allan- 

 tois. Furthermore, as Prof. Huxley has pointed out*, the hyoidean 

 and mandibular arches are, in these groups, " suspended by a pedicle 

 or suspensorium, which is, to a certain extent, common to both ;" 

 whereas in Reptiles and all remaining Vertebrates, the proximal 

 ends of the two arches are quite distinct. In sliort, the true Rep- 

 tiles possess in common the following series of characters by whicli 

 they may, without difficulty, be distinguished from Amphibians : — 



1. They are without gills. 



2. They are provided with an amnion and allantois. 



3. They do not exhibit those changes after birth which are so 

 characteristic of most recent Amphibia. 



4. Their tegumentary system presents peculiar features. 



5. They possess a single occipital condyle. 



6. As in other abranchiate Vertebrates, " the proximal end of the 

 hyoidean arch is quite distinct from that of the mandibular 

 arch." 



It seems scarcely necessary to add that the names of Agassiz f, 

 Von BaerJ, Bell§, Van Beneden||, De Blainville^, Carpenter**, 



* See his Croonian Lecture, " On the Theory of the Vertebrate Skull," in 

 Proceedings of the Eoyal Society, November 18, 1858. 



t Essay on Classification. London, 1859. 



X Ucber Entwickelungsgcscliichte der Tliiere. Konigsberg, 1828. 



§ History of British Reptiles, second edition. London, 1849. 



II In several of his works. See, however, his ' Zoologie Medicale,' published 

 in conjunction with Grervais. Paris, 1859. 



IF De I'organisation des Animaux. Paris, 1822. 



** In many of his works, but most recently in his ' Animal Physiology,' 

 new edition. London, 1859. 



