GREAT WESTERN BURROWING PROG, 



243 



a depression was dug in the ground and the eggs placed in a little hollowed-out 

 space aboul the size of a man's fist. This was covered over with soil to a depth of 

 about 1 foot, but a sheet of -lass formed one side of the nest. The eggs could he 

 seen therefore without disturbing them in the slightest. Alter three or four .lays 

 embryos were well advanced, and external gills could be observed. There was. 

 however, no sign of hatching. During the following days the external gills were 

 further developed, and then replaced in the usual manner by internal gills. The 

 embryos grew steadily, remaining coiled round the yolk sac on the surface of 

 which blood vessels were very distinctly visible. 



About three to four weeks alter the laying oi the eggs, a few of the em- 

 bryos were placed in a dish and fresh water added. They hatched out in a few 

 minutes. These specimen- were kept for a month longer, during which time 

 they gradually developed. The other collections of embryos, including those in the 

 garden observation nest, were, however, still unhatched. The yolk sac had com- 

 pletely disappeared external -ills had vanished, and the operculum had grown 

 completely over the gill slits. The embryos were pigmented and well advanced. 



Three stages in the development of Heleioporus albopunclatus. The figure on the right 

 represents the stage at which hatching took place. 



Further development became slow, and practically no further external changes 

 were to be seen at the age of six or seven weeks — probably two months in some 

 cases, when a tragic occurrence (from the point of view of the Amphibia) pu1 a 

 complete end to the experiments. During the whole period (from the first trial 

 at the end of three weeks until the end of the seventh week ) the addition of water 

 to any embryos caused them to hatch at once. In some cases the water was re- 

 moved afterwards and the tadpoles allowed to lie in the moist sand. They lived 

 covered with soil for two or three days. It was nol possible owing to other busi- 

 ness to experiment carefully with them, and they dried up. It would be interest- 

 ing to know how long the hatched tadpoles could live in a moist atmosphere with- 

 out actual water, provided that moulds, etc., did not develop. 



Thus in the early stages of the life history of the West Australian Burrowing 

 Frog we have an example of a large heavily-yolked es;g with an embryonk- de- 

 velopment which may progress to a rather advanced stage without hatching. So 

 far as is known at present, there is no tendency to go beyond a stage in which 

 legs are not visible externally. Hatching had not taken place at the end of seven 

 weeks, and probably a longer period than this had elapsed in the case of some 

 undisturbed examples. The retention of the larva within the egg membrane is 

 evidently controlled by the presence or absence of water. 



There is perhaps some reason for mentioning the occurrence that put an end 

 to all the experiments. My house is situated very close to the Swan River. One 

 Sunday a heavy gale arose from the south-west, and at the same time an un- 

 usually high tide occurred. The combination resulted in a rapid rise in the river 

 until waves commenced to break over on the lawn. At about 10 a.m. the bare 

 area where the frogs lived was being flooded. The water was only brackish. At 



