238 



CHAPTERS ON EVOLUTION. 



proteus and axolotl, &c., have retained many of their lower cha- 

 racters most notably gills and tail and have accordingly taken a 

 lower and less modified position than the frogs and toads. The 

 familiar tailed newts (Fig. 161), which, though living in water, 



and beginning life as 

 gill-bearing tadpoles, 

 breathe as adults, by 

 lungs alone, represent 

 a middle term in the 

 series, in that they still 

 retain the larval tail of 

 early life. 



Whilst the ordinary 

 course of amphibian 

 development runs as 

 has just been described, 

 there are certain excep- 

 tions of extreme interest 

 from the evolutionist's 

 point of view. Firstly, 

 there are certain cases 

 of curious development 

 amongst the frogs them- 

 selves, which deserve a 

 passing notice. There 

 are peculiarities, for in- 

 stance, in the carrying 

 of the eggs, which are 

 eloquent enough in 

 their testimony to the singular modification of structure and habits 

 which may accompany alteration of surroundings. Thus the tadpole 

 form of Pstudis paradoxa attains a very much larger bulk than the 

 adult. Such a circumstance points either to some nutritive condition 

 affecting the larva, or shows that the larva reproduces some ancestral 

 form which was larger than the living frog. The female of Nototrema 

 marsupiatum, a tree-frog inhabiting America, carries her eggs in a 

 large pouch which underlies the skin of the back, and opens behind. 

 The larva of Nototrema are said to want external gills. If correct, 

 this circumstance points to high modification in the development 

 of this frog. A like feature to the method of egg-carrying found 

 in Nototrema is seen in Opisthodelphys, another American frog ; and 

 Hylodes, likewise an American tree-frog, lays its eggs in the axils of 

 leaves that is, in the angle between leaf-stalk and stem the water 

 needful for their development being found in the chance drops resting 

 in that situation. The male of Alytes obstetricans of Europe, winds 



FIG. 161. NEWTS. 



