10 



PROF. AGASS1Z S 



[PLATE V.] 



presence or absence of a tail, these have been divi- 

 ded into two groups without a tail and with the 

 tail. The tail is shorter and thicker and the whole 

 body is more contracted. [Plate V. fig. B.] Here are 

 gills which do not exist in any other of this group, 

 gills which exist in the whole life only with fishes; 

 but which here exist simultaneously with lungs in 

 the body. This is called [fig. B] Menobranchus 

 Maculatus; and this [fig. A] is called Menopoma 

 Alleghaniensis^ 



[PLATE VI.] 



Here are three fingers forward and two back- 

 ward. [Plate VI. fig. A.] This is found in South- 

 ern Germany. Here [fig. B] is one with a very 

 minute fin. This is a species which occurs in Geor- 

 gia. And here is an animal [fig. C] which has 

 anterior legs but no posterior ones, and occurs in 

 our Southern Slates. There is another type which 

 is not figured, in which there is no tail, no legs, 

 and only a transient and temporary gill. It is the 

 Csecilia the so called naked snake. The position 

 which is now assigned to these different an- 

 imals is as follows : As late as 1826, Fitzinger, 

 who has furnished an elaborate dissertation on 

 this class of reptiles, classes at the head of Batra- 

 chians the genus Ccecilia, still impressed with its 



resemblance to the snake. He considered it as al- 

 lied to the snake and placed it at the head of Ba- 

 trachians, which are from their structure the low- 

 est type among reptiles. Next he placed the frogs 

 and toads, then the salamanders, and those ani- 

 mals next these, like salamanders [Plate V. fig. B.J 

 This was followed by all following investigators 

 of succeeding years. Cuvier, in his animal king- 

 dom, in 1829, however, made a step backward. He 

 replaced the Caecilia among snakes, though he 

 could not have overlooked the investigations of 

 naturalists who had shown that the want of ribs, 

 the peculiar articulation of the head with the 

 trunk, was much more closely allied to that of 

 frogs than to that of snakes ; and the want of mov- 

 able jaws, again, should have prevented him from 

 confounding the Cecilia with snakes. 



He placed the frogs at the head, next the toads, 

 next the salamanders without external gills, and 

 finally the salamanders with external gills. I have 

 given these details on purpose to show that in 

 all these methods there is no principle ; and I refer 

 to the leading authors in the natural history of 

 reptiles in order that I may not be taxed with over- 

 rating the value of the principle which I am now 

 about to introduce, or of over-rating its influence 

 its value. Wagler, who is also the author of a 

 system of Herpetology, places at the head, caecilia, 

 next frogs, then toads, next salamanders, and final- 

 ly, the proteus and menobranchus. Canino fol- 

 lowed in a similar track; so did Johannes Miller, 

 of Berlin, who modified it somewhat, placing the 

 naked snake lowest. Next this one, which has no 

 external gills, [Plate VI. fig. B.] and finally this 

 one [Plate V. fig. A.] And above these he places 

 those which have gills, and above the salamanders, 

 the frogs. 



Tschudi, who has published a natural classifica- 

 tion entirely devoted to this subject that of Batra- 

 chians places Menobranchus lowest. Then he pla- 

 ces the naked snake between salamanders and frogs; 

 which he justifies simply from the structure of the 

 head, or at least, gives that as his reason for the 

 arrangement. Now you see that from want of 

 a principle, all these details differ in the various 

 authors. No one is ruled by anything but his im- 

 pressionhis feeling about it. And I think that 

 we can substitute a principle, and we can show 

 that this principle has nothing arbitra^, and is 

 given to us by nature. 



Let us trace the metamorphoses of frogs, and 

 there we have the key. What are the changes 

 which frogs and salamanders undergo ? In the be- 

 ginning,for instance, salamanders are animals with - 

 out legs at all, [Plate IV. fig. Aj with a long tail^ 

 and large gills on the side of the head. A change 

 takes place. [Fig. B.] Another change occurs; the 

 gills remaining and growing larger, when an 

 anterior pair of legs appears, and in anoth- 

 er stage the gills are reduced 1 Figs. C. D ] when 

 the second pair of legs appears. [Fig. E J Here the 

 anterior pair has four fingers, but here [Fig. F] is a 



