568 GEORGTNA SWEET. 



the struggle for room or food may maintain themselves for a 

 long time. 



Eigenmann [1, pp. 600^ 601] doubts the eflBcacy of the 

 struggle for room and food in the degeneration of the eyes of 

 the Amblyopsidee, since the position and room formerly occu- 

 pied by the eye is now filled with fat. But in Notoryctes we 

 found very little fat, and that only in one specimen, while on 

 the other hand the more degenerate the eyeball itself the 

 more highly developed the gland arrangements were found 

 to be. 



As to the object of the burrowing of the animal we must 

 conclude that it is mainly for food, as suggested in the Horn 

 Expedition Report, and as a means of escape from its 

 enemies. 



The loss of the eye as a means of knowledge of the external 

 world is compensated for by the great sensibility of the animal 

 to sound, and probably from the presence of the supposed 

 tactile sense-organs to touch. 



Its relation in point of degeneracy to Scalops and Talpa is 

 interesting, since we may regard it in two ways. Either the 

 eye of the Marsupial has had a longer time since it took to 

 buiTOwing life in which to become reduced than has that of 

 the insectivorous European Talpa or American Scalops, or, 

 more probably, the sand in which Notoryctes lives is, and has 

 been, more deleterious to the eye than the earth in which 

 Scalops and Talpa burrow, and so degeneration has gone on 

 more quickly in Notoryctes. 



Professor Spencer suggests that this view is strengthened 

 by the evidence as to the recent past of Central Australia. 

 There we find deep gorges and broad river valleys compara- 

 tively intact, though now dry except on rare occasions, show- 

 ing that this region was favoured with a more liberal rainfall 

 at no very great distance of time. Then when the conditions 

 became dryer the decomposition of the rocks and the wearing 

 of their debris produced a finer and finer sand. Probably, 

 up to this time, Notoryctes was a burrower with its eyes in a 

 condition comparable to those of Talpa, and as the sand be- 



