LECT. III.] NEWTS AND FROGS. 87 



The eggs are very large, and in this pouch, which they enormously 

 distend, they undergo their development. A more or less similar 

 pouch is found in Nototrema marsupiatum}- 



11 In the Surinam Toad (Pipa dorsigera), the eggs are placed by the 

 male on the back of the female. A peculiar pocket of skin becomes 

 developed round each egg, the open end of which is covered by a 

 gelatinous operculum. The larvae are hatched, and actually undergo 

 their metamorphosis, in these pockets. The female during this 

 period lives in water. Pipa americana (if specifically distinct from 

 P. dorsiyerd) presents nearly the same peculiarities. The female of 

 the Tree Frog of Ceylon (Polypedates reticulatus) carries the eggs 

 attached to the abdomen. 



" Rliinoderma Darwinii behaves like some of the Siluroid fishes 

 in that the male carries the eggs during their development in an 

 enormously-developed laryngeal pouch. 



" Some Anura do not lay their eggs in water. Cliiromantis 

 guineensis attaches them to the leaves of trees ; and Cystignathus 

 mystacius lays them in holes near ponds, which may become filled 

 with water after heavy rains. 



The eggs of Hylodes martinicensis are laid under dead leaves in 

 moist situations." Balfour's Embryology r , vol. ii. p. 100. 



Now, if Bees " teach the order of a peopled kingdom," so also do 

 Frogs and Toads suggest to us all sorts of skilful ways of keeping a 

 family from want and danger. 



But in no case, yet, have we in this survey come across any type 

 that preserves its developing progeny ivithin itself, nourishing and 

 cherishing it, not merely as a nursing mother does her child, but as 

 the same mother does while that child is still invisible. 



That method is nature's most motherly invention. Does she give 

 any prophecy that shows any beginnings of this exquisitely gentle 

 forethought in the cold tribes of the waters ? 



A good time before our era Aristotle discovered that certain 

 sharks have this habit. " Mustelus levis (the smooth hound, as the 

 sailors call it), which is one of those in which development takes 

 place within the uterus, presents a remarkable peculiarity in that the 

 vascular surface of the yolk-sack becomes raised into a number of 

 folds, which fit into corresponding depressions in the vascular walls 

 1 Here, certainly, the pouch opens behind. 



