218 SCIENCE FROM AN EASY CHAIR 



tadpoles in a pond near Antwerp, and thought they must 

 be a realisation of Dr. Edwards' experiment. They were 

 enormous, and it was only on bringing them home that 

 I heard for the first time of the spur-heeled toad and its 

 gigantic tadpoles (Fig. 44 C). 



Among frogs and toads from distant lands are some 

 which bring forth their young alive, the female retaining 

 the eggs in her body instead of laying them in water. 

 The black-and-yellow salamander of Europe (which, like 

 the common toad, has a highly poisonous secretion in 

 the skin) retains its eggs inside its body until the 

 tadpoles are well advanced in development, when they 

 pass from her about seventy in number into the 

 water. In the closely allied black Alpine salamander 

 only two, out of thirty or more eggs produced, develop. 

 These two remain inside their mother until they have 

 ceased to have gills and have become terrestrial air- 

 breathing young salamanders like their mother. The 

 Alpine salamander lives where there are no pools suitable 

 for the tadpoles, and so they never enter the water, but 

 remain inside the mother's body. Some experiments 

 have recently been made with these two species of 

 salamander by varying the conditions as to moisture in 

 which the young grow to maturity, and results of con- 

 siderable interest have been obtained. One of the most 

 curious arrangements in regard to the young is seen in 

 the Surinam toad, of which we had living specimens five 

 or six years ago in the London Zoological Gardens. In 

 this toad the skin of the female's back becomes very soft 

 and plastic at the breeding-season. As she lays the 

 eggs the male takes them one by one and presses them 

 into the soft skin of her back, into which they sink. 

 The eggs are thus embedded separately to the number 

 of fifty or sixty, each in a little pit in the mother's back. 

 They slowly develop, each in its "pit," the orifice of 



