268 NATURAL SCIENCE. Oct., 



in all the aquatic larvas of Amphibia, and persist in those Urodela 

 which lead an aquatic life, e.g., Proteus, Molge. They are lost in adult 

 Anura, except Xenopns and some Pelobatoids, and in those Urodela, 

 e.g., Salamaiidra, which are terrestrial when adult.' Examples : 

 Pelodytes tadpole and adults of Xenopns and Molge. 



Development. — ' The Anura are oviparous, and the larvae or 

 tadpoles, when hatched, soon develop a tail provided with a fin. A 

 pair of suckers are in some cases developed on the ventral surface 

 behind the mouth, which latter is provided with horny teeth. 

 Respiration is at first effected by means of three pairs of external 

 gills, and later by internal gills, developed on the walls of the four 

 branchial clefts. An atrial membrane grows back over the gill- 

 clefts and, on the closure of the exhalent aperture, pulmonary 

 respiration is definitely established. The limbs are formed com- 

 paratively late, and the tail, which is supported by a notochord and 

 not by vertebrae, is gradually absorbed.' Below this label is a 

 gradational series of twenty tadpoles of the common frog, showing 

 the development from the egg up to the completion of the meta- 

 morphosis. ' The spiracle or exhalent aperture of the branchial 

 chamber is, in most tadpoles, situated on the left side of the body, 

 but in Xenopns it is paired, and in the Discoglossida; it is situated on 

 the ventral surface.' Examples: tadpoles oi Alytes, Rana, Pelohates, 

 and Xenopus. 



Then follow five skeletons of Pelohates at different stages of 

 development, and attention is called to the following points of 

 interest : — ' Vertebras are not formed around that portion of the noto- 

 chord which supports the large swimming tail of the tadpole, and this 

 caudal notochord is gradually absorbed as the tail becomes reduced 

 in size in the metamorphosis from the tadpole to the adult form. 

 The greater part of the urostyle of the adult is formed from a splint 

 of bone developed on the ventral surface of the notochord behind the 

 last vertebra. There is a gradual increase in size and in the extent 

 of ossification of the skeleton of the limbs and the limb-girdles, and 

 the pelvis becomes connected with the vertebral column. There is 

 also an increase in the breadth of the skull and the size of the mouth, 

 and the branchial skeleton becomes greatly reduced.' 



' The larvae of Urodela possess external gills, which may be 

 retained by the adult {e.g., Proteus) or lost (newts and salamanders). 

 The tail persists and develops complete vertebrae.' Example : larva 

 of Salamandra maculosa at birth. ' The larvae of Apoda possess 

 external gills and a tail which is absorbed more or less completely 

 during metamorphosis.' Example : larva of Ichthyophis showing 

 external gills, tail, and yolk-sac. 



At the foot of this column the dimorphism of Amhlystovia is 

 illustrated by the exhibition of a typical Axolotl and a perfect or gill- 

 less form of about the same size, with the following description : — 

 ' This Amphibian is dimorphic, a condition very uncommon in verte- 



