44 DEVELOPMENT AND HEREDITY. 



whole system of medicine rests upon the fact that 

 certain elements taken into the body have power 

 to influence the growth, or repair, or development, 

 of the different organs of the body. The effect 

 of a change of food is shown by Daubenton's state- 

 ment that the intestine of the domesticated cat 

 is considerably longer than that of the wild cat. 

 One of the most striking facts of this connection 

 is that reported by Dr. Born, and also by Professor 

 E. Yung, in regard to the influence of food on the sex 

 of tadpoles. According to these experiments,^ the 

 feeding of an unmixed diet to the larvae until after 

 their metamorphosis, has a tendency to produce 

 females. Among 1443 tadpoles thus fed until after 

 metamorphosis, and then examined by Dr. Born, 

 ninety-five per cent were found to be females and 

 five per cent males. These were raised in a num- 

 ber of different aquaria, and in some of the aquaria 

 the proportion of females was one hundred per cent. 

 In one of Dr. Born's aquaria, which received acci- 

 dentally a mixture of diet, the males were found 

 in the proportion of twenty-eight per cent. These 

 latter specimens were also larger, approaching, in 



1 G. Born, " Experimentelle Untersuchungen ueber d. Entstehung 

 d. Geschlechtsunterschiede," Breslauer iirtzlicher Zeitschrift, 1881. 

 E. Yung, " De I'influence des milieux physico-chemiques sur les etres 

 vivants," Archives dcs Sciences physiques et natiirelles, Mars, 18S2, 

 troisieme periode, tome vii. 



