142 



URODELA. 



op 



long processes (j), like the suctorial processes in Triton, placed on the throat 

 in front of the external gills. They are used to support the larva when it 

 sinks to the bottom, and have been called by Clarke (No. 98) balancers. On 

 the development of the limbs, 

 these processes drop off. The 

 external gills atrophy about one 

 hundred days after hatching. 



It might have been anticipated 

 that the Axolotl, being a larval 

 form of Amblystoma, would agree 

 in development with Amblystoma 

 punctatum. The conspicuous suc- 

 torial processes of the latter form 

 are however represented by the 

 merest rudiments in the Axolotl. 



The young of Salamandra 

 maculata leave the uterus with 

 external gills, but those of the 

 Alpine Salamander (Salamandra 

 atra) are born in the fully de- 

 veloped condition without gills. 

 In the uterus they pass through a 

 metamorphosis, and are provided 

 (in accordance with the principle 

 already laid down) with very long 

 gill-filaments 1 . 



Salamandra atra has only two 

 embryos, but there are originally 



a larger number of eggs (Von Sie- 

 ,,,,,.,.,,. f ., . 



bold), of which all but two fail to 



develop, whi,e their remains are 



used as pabulum by the two which 



survive. Both species of Sala- 



mander have a sufficient quantity of food-yolk to give rise to a 



sack. 



Spelerpes only develops three post-hyoid arches, between which slits are 

 formed as in ordinary types. Menobranchus and Proteus agree with 

 Spelerpes in the number of post-hyoid arches. 



One of the most remarkable recent discoveries with reference to the 

 metamorphosis of the Urodela was made by Dumeril 2 . He found that some 

 of the larvae of the Axolotl, bred in the Jardin des Plantes, left the water, 

 and in the course of about a fortnight underwent a similar metamorphosis to 

 that of the Newt, and became converted into a form agreeing in every 



1 Allen Thomson informs me that the crested Newt, Triton cristatus, is in rare 

 instances viviparous. 



- Comptes RenJits, 1870. 11.782. 



FlG - 84. LARWE OF AMBLYSTOMA 

 PUNCTATUM. (After Clarke.) 



yolk- 



