STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 2O7 



each tier of trays; and by means of small stop-cocks each dish 

 is supplied with running water. The depth of the water in the 

 trays is kept at about two inches by means of constant level 

 siphons, the water running from each siphon into a trough that 

 empties into a large exit pipe. By the use of this apparatus 

 large numbers of eggs, subjected to very different influences at 

 the time of fertilization, can be reared under similar external 

 conditions. Marked variations in the results of the several 

 series of experiments must be attributed to the different conditions 

 under which the eggs were fertilized; they cannot be due to 

 differences in the environmental conditions under which the 

 embryos developed. 



The apparatus described above was used for all of the 

 experiments made during the spring of 1910. An abundant 

 supply of varous kinds of water plants was always kept in the 

 dishes containing the tadpoles. All of the tadpoles received 

 similar food, which consisted of small pieces of cooked meat or 

 of frog muscle, yolk of egg, cereal and so-called "fish food." 

 The water was allowed to run slowly in each dish for about six 

 hours every day, and was then turned entirely off at night to 

 prevent a possible accident through a change in the water pres- 

 sure. To prevent any loss of tadpoles through a fouling of 

 the water by food and impurities that could not be carried away 

 through the siphon, the inner end of which was covered with 

 fine netting, each dish was thoroughly cleaned once a week 

 during the first month after the experiment was started, and much 

 oftener when the tadpoles had become larger and the weather 

 warm. 



As many as possible of the individuals used in each series of 

 experiments were carried through to metamorphosis and their 

 sex ascertained: the methods used in ascertaining sex being the 

 same as those previously employed (King, '07). 



In the various tables given in this paper the figures in the 

 second column refer in every case to the number of individuals 

 alive one week after the experiment began; they do not indicate 

 the number of eggs that were subjected to the unusual conditions 

 at the time of fertilization. In investigations of this kind it is 

 very important, as I am fully aware, that the mortality in the 



