Salamandra atra has only two embryos, but there are originally a larger number of eggs (Von Siebold), of which all but two fail to develop, while their remains are used as pabulum by the two which survive. Both species of Salamander have a sufficient quantity of food-yolk to give rise to a yolk-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[58]. He found that some of the larvæ 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 particular with the American genus Amblystoma. During this metamorphosis a pulmonary respiration takes the place of a branchial one, the gills are lost, and the gill slits close. The tail loses its fin and becomes rounded, the colour changes, and alterations take place in the gums, teeth, and lower jaw. [58] _Comptes Rendus_, 1870, p. 782. Madame von Chauvin[59] was able, by gradually accustoming Axolotl larvæ to breathe, artificially to cause them to undergo the above metamorphosis. [59] _Zeit. f. wiss. Zool._, Bd. XXVII. 1876. It seems very possible, as suggested by Weismann[60], that the existing Axolotls are really descendants of Amblystoma forms, which have reverted to a lower stage. In favour of this possibility a very interesting discovery of Filippi's[61] may be cited. He found in a pond in a marsh near Andermat some examples of Triton alpestris, which, though they had become sexually mature, still retained the external gills and the other larval characters. Similar sexually mature larval forms of Triton tæniatus have been described by Jullien. These discoveries would seem to indicate that it might be possible artificially to cause the Newt to revert to a perennibranchiate condition. [60] _Zeit. f. wiss. Zool._, Bd. XXV. sup. 1875. [61] _Archivio per la Zoologia, l'Anatomia e la Fisiologia_, Vol. 1. Genoa, 1861. Conf. also Von Siebold, "Ueber die geschlechtliche Entwicklung d. Urodelen-Larven." _Zeit. f. wiss. Zool._, Bd. XXVIII., 1877. Gymnophiona. The development of the Gymnophiona is almost unknown, but it is certain that some larval forms are provided with a single gill-cleft, while others have external gills. A gill-cleft has been noticed in Epicrium glutinosum (Müller), and in Coecilia oxyura. In Coecilia compressicauda, Peters (No. 108) was unable to find any trace of a gill-cleft, but he observed in the larvæ within the uterus two elongated vesicular gills. BIBLIOGRAPHY. _Amphibia._