124 CHARLES R. STOCKARD 



attempted to refute the slow rate as a cause of structural modi- 

 fication in discussing my assumption of arrested development. 

 The present experunents differ from the previous temperature 

 experiments in that they were undertaken with an almost 

 completely different problem in view. The former experiments 

 will be considered only as they bear on the specific questions in 

 the discussion to follow. 



Numerous studies on the behavior of eggs deprived of oxygen 

 as well as in the presence of various reducing and anaesthetic 

 substances have been conducted. All of these oxygen studies 

 have little or no bearing on the immediate problems and are not 

 treated in this connection. 



The material used in the present experiments were the eggs 

 of the common minnow Fundulus heteroclitus. I have studied 

 and experimented with these eggs for a number of years and am 

 familiar with a great many common deformities which they may 

 be induced to present. The exact method of experimentation 

 with temperature change was as follows: the eggs were taken 

 from the female and fertilized in a 'dry bowl.' About fifteen 

 minutes later they were rinsed free of foreign material with sea- 

 water and left standing under water. The first cleavage takes 

 place after about two hours, varying a little with the season and 

 \ the temperature. The next cleavage follows after another hour, 

 and development proceeds in a continuous fashion from then on 

 until the fully formed fish hatches from the egg membrane and 

 wims freely about within from eleven to eighteen or twenty 

 ays, depending again upon the season and temperature. There 

 s a wide variation in the rate of development of these eggs, yet 

 nder all usual conditions after development once starts it is 

 continuous. 



The eggs were placed during different stages of development in 

 compartments of a refrigerator at temperatures of 5°, 7° and 9°C. 

 and left for varying lengths of time, from one to five days. At 

 the lowest temperature development was almost if not completely 

 stopped, while in the other two compartments it was slowed 

 idown to from one-twentieth to one-fiftieth of the normal rate. 

 The responses shown in the manner of development are so differ- 



