THE TALE OF TADPOLES 39 



the way it feeds as an adult, e.g. on beetles much too large 

 for it, is often far from saying much for its varied gas- 

 tronomic education. 



And again, as regards the fundamental problem of 

 breathing, we find the newly hatched tadpole breathing 

 through its skin in the old-fashioned manner of earthworm 

 and leech ; then follow in succession, the first set of 

 external gills, the gill-clefts, the second set of external gills, 

 which are usually called internal ; then follows a period 

 with gills and lungs together ; then there is the transition 

 to terrestrial life with pulmonary and (retained) cutaneous 

 respiration ; finally, in winter, the hibernating frog, 

 retiring into the mud-fortresses of its remote ancestors, 

 breathes by its skin only. 



Several experimenters have found that the numerical 

 proportion of the sexes in frogs appears as ij it were modi- 

 fiable by changes in the nutrition. Thus Professor Yung, 

 of Geneva, fed tadpoles with minced beef, and found that 

 the percentage of females was 78, instead of 54 as in the 

 control set in natural conditions. He fed another set with 

 fish flesh, and the percentage rose to 81, as against 61 in 

 the control set. In a third set, to which the flesh of frogs 

 was supplied, the percentage rose from 56 to 92 ! It has 

 to be noted, however, that subsequent experimenters have 

 not confirmed these results, which are also open to the 

 fatal objection that the sex of those tadpoles that died 

 was not determined. It may have been that the change 

 of diet affected the males prejudicially and favoured the 

 survival of females. While the results of the experiments 

 cannot, without further inquiry, bear the interpretation 

 originally put upon them, they are still interesting, even 

 if due to differential mortality. It is a well-known fact 

 that in some places, in natural conditions, the percentage 

 of females is very high, though 57 seems to be the average. 



