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the cage, it does not lay its eggs, but retains them until the young 
ones are developed. The difference between animals producing 
living offspring and those laying eggs is here effaced simply by the 
change of the ground upon which the animal lives.”—(Haeckel. 
The History of Creation. 3rd ed., vol. i., p. 240.) 
“Allen Thomson informs me that the Crested Newt (Triton 
cristatus) is in rare instances viviparous.”—(Balfour. A Treatise on 
Comparative Embryology, vol. ii., p. 142—note.) 
In the next place, we may observe the phenomenon which 
Kollman calls Neotenia—or the lengthening for an in 
definite time of the period during which larval amphibians 
remain gill-breathers. 
“ When tadpoles were placed, by Dr. Milne Edwards, in a per 
forated box, sunk in the Seine, . . . they grew to a great size in 
their original form, but they did not pass through the usual metamor 
phose which brings them to their mature state as frogs.”—(Chambers. 
Vestiges. 4th ed., p. 238.) 
The explanation of this fact is not, as the author of 
Vestiges seems to think, “ light being the only condition 
thus abstracted,” but rather that the tadpoles were kept 
from rising to the surface and coming into contact with 
the air. This inference is confirmed by what takes place 
sometimes in connection with the proteus. 
“ The proteus is furnished with branchiae as well as with lungs, and 
Schreibers found that when the animal was compelled to live in deep 
water, the branchiae were developed to thrice their ordinary size and 
the lungs were partially atrophied. When, on the other hand, the 
animal was compelled to live in shallow water, the lungs became 
larger and more vascular, whilst the branchiae disappeared in a more 
or less complete degree.”—(The Variation. 1st ed., vol. ii.,p. 297.) 
Another cause of the arrested development of larval 
forms would seem to be a deficiency of food. Dr. Henry 
de Varigny says :— 
“ I have myself kept toads in the tadpole state for over two years, 
merely by feeding them very scantily. They were born in the spring 
of 1889, and remained all the time in an aquarium in the laboratory,