394 



V. Near c tic Region. 



Characteristic forms. — Scaphiopus, Acris, Pseudacris,Notophthal- 

 mus, Taricha, Xiphonura, Ambystoma, Cylindrosoma, Desmoyna- 

 thus, Desmodactylus, Batrachoseps, Spelerpes, QZdipus, JEnsatina, 

 Axolotes, Protonopsis, Amphiuma, Menobranchus, Siren, Pseudo- 

 branchus. 



Forms common with other regions. — Cystignathus, Engystoma. 



Schlegel, by trying to establish parallels between North and South 

 America, was, I think, unfortunate in looking for respective repre- 

 sentatives of both regions: parallels may be established between the 

 Palsearctic and Nearctic region which are far more true and inter- 

 esting. 



If we allow 20 species of Anura and 50 of TJrodela for this 

 region, we have on an average one species to every 90,000 square 

 miles, or about three species for the same area for which we found 

 only one in the Palsearctic region. This greater abundance is due 

 to a greater number of Anura as well as of Urodela ; but if the 

 Nearctic region has three times as many Anura as the Palae- 

 arctic in proportion to its area, it yet produces four times as many 

 Urodela. 



By repeated examinations of a great number of specimens I have 

 convinced myself that the North American frog, called Rana sylva- 

 tica, does not form a distinct species from the Rana temporaria of the 

 Old World. It is true that there may be found more differences than 

 those of colour only, by examining a few specimens (for instance, 

 in the size of tympanum) ; but if we look to a greater number of 

 specimens, and compare them especially with those from the eastern 

 parts of Asia, even those differences will be found to be levelled. 

 Among those species which are the most common we always find 

 the greatest variations in form and colour. Among the European 

 specimens themselves were found greater differences than those be- 

 tween European and American ones ; and naturalists were induced 

 to establish several species even for the European forms. The ex- 

 tremes of the variety Rana oxyrhina might be taken at the first 

 glance for Rana esculenta ; but on comparing them with other spe- 

 cimens of the same locality, we soon come to the point where it 

 is impossible to decide to what form the specimen belongs. Like- 

 wise any naturalist, before whom might be placed one of the above- 

 mentioned specimens from Eastern Asia, would be at a loss to de- 

 termine whether it were from the Old World or from the New. But 

 are we at liberty to separate species or genera only according to the 

 soil where the beings are born, without finding sufficient external or 

 better anatomical characters ? As the palaeontologist endeavours to 

 show what organic forms reappear in a stratum above or below an- 

 other, and where a new creation begins, so the zoologist must do in 

 the horizontal distribution of animals on the earth's surface. Our 

 Rana esculenta is represented by Rana halecina : specimens of the 

 former exhibit sometimes quite the same coloration as that con- 

 stantly found in R. halecina ; but they invariably differ in the struc- 



