372 Prof. J. van der Hoeven on the Genus Menobrauchus 



which there are sixteen or seventeen vertebrae between the skull 

 and the pelvis. 



We must therefore guard against expressing this relation 

 too strongly ; and^ while asserting that the nearest affinity of 

 the Menobranchus is probably with Proteus, we must, at the 

 same time, admit it as intermediate between this and Crypto- 

 branchus. I should incline even to regard Menobranchus as oc- 

 cupying the central position in the ichthyoid group. In fine, 

 we have in the present only another instance of what nearly 

 always occurs in families and groups composed of but few spe- 

 cies, and these spread over various and remote countries : there 

 are almost as many genera as species; and, in spite of the com- 

 mon bond of affinity, there is a very marked difference in the 

 general form and in the proportions of the body and its parts. 



Those who would prefer to dispose the genera in a single 

 series, might perhaps do so by allowing Siren to follow Cacilia, 

 and the Axolotl to occupy a corresponding position on the other 

 side leading to the Salamanders (Urodela with eyelids) . The 

 ichthyoids afford a very interesting illustration of the proposi- 

 tion that some animals present as permanent a form which is 

 only transitory in others ; and Lamarck might have said that, 

 in the Axolotl, nature was on the point of forming the Triton. 

 Cuvier already in 1807 made use of the happy expression larve 

 permanente ; and it was in accordance with this that he said that 

 the Siren might be regarded as a permanent larva of this family*. 



We should thus have the following succession : — 



Siren, 



Amphiuma-f, 



Proteus, 



Menobranchus, 



Cryptobranchus, 



Sirenodon, 



since at Rotterdam, the pelvis was found to be suspended, on the right, 

 from the twentieth, and on the left from the twenty-first vertebra. (Aan- 

 teekningen over de Anatomic van den Cryptobranchus japonicus, door Dr. 

 F. J. J. Schmidt, Di*. Q. J. Goddard en Dr. J. van der Iloeven, Jun. : 

 Haarlem, 1862, 4to, p. 11.) The authors of this memoir cite an observa- 

 tion of C. A. Schultze, attesting a similar inequality or asymmetry as ob- 

 served in the skeleton of a Triton cristatus. They might also have added 

 that the anatomist Mayer had recorded a like circumstance with regard to 

 the other species of Cryptobranchus, that from the AUeghanies. Although 

 it would seem to be normal in this species that the pelvis be thus suspended 

 from the twentieth vertebra, Mayer observed, in one of the skeletons pre- 

 pared by him, that it adhered only on the left side to this vertebra, but on 

 the right to the nineteenth (Analecten, &c. p. 78). 



* Recherches sur les Reptiles douteux, p. 109. 



t These two genera depart more particularly from the true Salamanders 



