432 J. F. GUDERNATSCH 



The eggs of these species were collected from ponds in the vicin- 

 ity of Munich and reared in the laboratory. They were kept 

 in large aquaria and after hatching were transferred to smaller 

 dishes, each dish containing about 100 individuals. After the 

 larvae had grown for some time and seemed to be crowded in the 

 dishes they were separated into smaller groups. To avoid pos- 

 sible errors, a great number of individuals was always used for 

 each kind of experiment. All in all, over 20.000 tadpoles were 

 treated. 



The eggs from different localities were kept separate and, as 

 far as possible, eggs apparently coming from the same mother were 

 grouped in one set and used for a special experiment. When- 

 ever the eggs necessary for one experiment could not all be sup- 

 plied by a single female I endeavored to select eggs coming from 

 the same locality, and apparently in the same stages of develop- 

 ment. For example, set III probably contained eggs from three 

 mothers, but the time of hatching, April 7 and 8, and their 

 sizes, 10 to 11.5 mm at the beginning of the experiment, show 

 them to be in similar stages of development. Again, for other 

 experiments in which a large number of animals was required, as 

 in sets VIII to XI over 4000, several sets in apparently the same 

 stage of development were thoroughly mixed and then divided 

 into smaller groups. In these last sets the tadpoles hatched be- 

 tween April 10 and 13 and a month later, when the feeding 

 b^gan, their sizes varied from 13 to 18 mm; this difference is not 

 greater than one would encounter in eggs from a single individual. 



The water was changed at least once a day. While standing, 

 its temperature varied with the room temperature, a process that 

 corresponds to natural conditions. However, even in a room 

 with apparently uniform temperature, the water will not show 

 exactly the same temperature in all the dishes, as Barfurth has 

 pointed out. To overcome any unequal influence of light, air 

 and temperature resulting from the position of the dishes, they 

 were shifted several times a day so as to progress in a certain 

 order. With this precaution there were no detectable differences 

 of temperature in the dishes assigned to one set. There was 

 sometimes a slight difference of temperature between the dishes 



