xi DIPNOI, AMPHIBIA f,G7 



Mini its ric.hiii-ss in yolk and there is no group of Vertebrates 

 which offers anything like the same facilities for studying the 

 influence of yolk upon the course of development. Further it will be 

 only after greatly extended studies on different species that we shall 



be in a position to 



have a really com- 

 prehensive idea of 

 typical Anuran 

 development. 



Many tropical 

 species of Frogs 

 and Toads are to be r 



, . , ,. Fia. 251. String of eags ot unknown frog from the Gambia. 



Obtained allVe irom individual variations in the rate of development are indicated 

 animal dealers and l>y the varying size of the yolk-plug. 



in these it may be 



taken as a general rule that breeding takes place at the commence- 

 ment of the rainy season, or in other words when environmental 

 conditions become favourable after a prolonged period during which 



they have been unfavourable. By bear- 

 fj c ing this principle in mind such tropical 



amphibians may usually be induced to 

 breed in captivity. Bles in his excellent 

 f account of the life -history of Xenopus 



(1905) describes a method which will be 

 found to be of general use. The pair of 

 ^ animals were kept in a Budgett tropical 



aquarium consisting of a glass bell-jar 

 20 inches in diameter dipping into a 

 galvanized iron water-tank heated by a 



I 





small Bunsen burner and oxygenated by 

 plants of Vallisneria. During summer 

 the temperature of the water in the bell- 

 jar was kept at about 25 C. The water 

 was not changed. The frogs were fed 

 daily with small earthworms or thin 

 strips of raw calf's liver until they would 

 ft/ eat no more: In December the tempera- 



ture was allowed to fall to 15-16 during 



i h, -j.vj. Embryo of PI, nil, medusa the day and as low as 5-8 during the 

 oTitmf' attened out in night> A s the temperature rose with the 



onset of spring the frogs became more 



b.c, buccal cavity ; W, blastopore ; ,. i & , 6 n .1 i ^i 



me,, mesoderm Ngmente! active, waking up out of the lethargic 



condition induced by the winter's cold. 



Breeding was induced by simulating the natural conditions of 

 the rainy season. The temperature was raised to about 22 C. 

 Each morning and evening about two gallons of the water was 

 drawn off, allowed to cool for twelve hours and then returned to 

 the aquarium in the form of a fountain of spray from the upturned 



