298 PHILOSOPHY OF ZOOLOGY. 



" With respect to the branchial structure, there is a re- 

 markable difference, not only as to form, but to texture, 

 between the arches of the proteus, and those of the siren 

 and larvae above mentioned. In the siren and larva?, the 

 branchial arches are four on each side, and their margins 

 are furnished with small points, in the proteus, there are 

 but three on each side, and these are smooth. The arches 

 of the proteus have an osseous structure, those of the si- 

 ren and larvae are cartilaginous. This difference did not 

 escape M. CUVIER, who, speaking of the proteus, says, 

 6 Tappareil osseux qui porte les branchies, est beaucoup 

 plus dur que ne Tavons trouve dans la sirene, et dans Taxo- 

 lotlS and in his anatomical description of the latter animal, 

 he farther says, ' Tappareil qui supports les branchies a 

 de grands rapports avec celui de la sirene, et je crois que, 

 lors de la metamorphose, il en reste une partie pour former 

 Tos hyoide de la salamandre. 4 ' Now, if the branchial arches 

 of the siren be, as M, CUVIER asserts, entirely cartilaginous, 

 although the cranium, the lower jaw, and the vertebrae, be 

 perfectly ossified ; and if these arches, both in form and 

 number, be similar to those of the axdloily which M. CUVIER 

 himself regards as a larva, may it not be presumed that 

 the former animal is a larva also ? If, farther, the bran- 

 chial arches of the proteus, which is a perfect animal, be 

 osseous, and entirely different from those of the siren and 

 all the larvae hitherto known, have we not in these facts the 

 strongest reasons for regarding the siren as an imperfect 

 animal, and, therefore, essentially different from the pro- 

 teus ? 



" With regard, next, to the organs of circulation, there 

 are, in the larvae of the frog and salamander, as many ar- 

 teries given off on each side by the trunk that springs from 

 the heart, as there are branchial arches, viz. four. In the 

 siren and axolotl (which have also eight branchial arches), 



