276 PROCEEDINGS OF THE ACADEMY OF 



2. Tn the important characters of tlie possession of brauchiEe, of maxillary 

 bones, and of ossified vertebrae, the tailed Batrachia presents a series of a ris- 

 ing scale, measured by their successively earlier assumption. Thus Salaman- 

 dra a t r a"' produces living young, which have already lost the branchiiB ; S. 

 maculosa living young with branchi.e ; Plethodou f produces young from 

 eggs which bear branchiae but a short time, and do not use them lunctionally ; 

 Desmognathns nigra uses them during a very short aquatic life ; D. f u sea 

 and other Salamanders maintains them longer, while Spelerpes preserves them 

 till full length is nearly reached. Finally species of Amblystoma reproduce 

 while carrying branchire, thus transmitting this feature to their young as an 

 adult character And it is a very significant fact that Spelerpes, which bears 

 branchiie longest, next to Amblystoma, is associated in the same zoological 

 region with a genus (Necturus) which differs from its fbur-toed Ibrni (Batra- 

 cliosepsj), in nothing more than the possession of the osseous and branchial 

 characters of its larva, in a permanent and rei)roducing condition. That this 

 is a genus, to be one day converted into Batrachoseps by an acceleration of its 

 metamorphosis, or that has been derived from it by the reverse process, I am 

 much inclined to believe. In support of this I quote tiie following examination 

 into the time of change of the species of Amblystoma from my essay on that 

 genus. § 



"The great difference between the different species, and between individuals 

 of the same species in this respect, may be illustrated by the following com- 

 parison between the size of the animals at the time of losing the branchiae 

 so far as known, and that to which they ultimately attain. 



Species. Size at loss of branchiae. 



In. Lines. 



A. jeffersonianum, 1 5-75 



A. punctatum, 1 10 



A. conspersum, 1 10-5 



A. opacum, 2 2 



A. texense, 2 1 



A. microstomum, 2 3-5 



A. talpoideur^, 3 (perhaps too large ) 



A. paroticum, 3 7-5 (not smallest.) 



"7 to 



(3 7 



A. tigrinum, -l ^ ^ 



{ 



A. mavortium. 



3 9-5 to 8 9 





 A. raexicanum, ? branchite persistent. 8 



The last s{)ecies, though not uncommon in collections, is not known to pass 

 through its metamorphoses in its native countrj', but reproduces as a larva, 

 and is therefore type of the genus Siredon of Wagler, Cuvier, Owen and others. 

 The larva of A. mavortium in like manner reproduces, but their offspring 

 have in the Jardin des Plantes and at Yale College undergone an early meta- 

 morphosis. || 



Here is a case where all the species but two change their generic chaiacters; 

 one changes them or not, according to circumstances, and one does not change 

 them at all. What are the probabilities respecting the change in the first set 

 of species ? 



* See Schreibers Isis, 1833, 527 : Koelliker, Zeitsclir. f. Wissensch. Zoologie, ix, 4l)4. 



■j- Baird Iconographic Encyclopfedia, Wyman, Cope. 



X See Cope, .Journ. Ac Nat. Sci., Phila., 1800. 



§ Proceed. Academy, 1807. 



li Through the kindness of Prof. Dumeril. I have received both larvae and adult of the 

 ppecies hero noted, and ob.^erved by liim. Tlie larva is as he states, Siredan lic/i'iioidcs of 

 Baird, while tlie adult is his Amblystoma ma vor t iu m, not A. tig r in uni (= /«?-(>/«//() 

 as also supposed by Dumeril. 



[Oct. 



