The Influence of External Factors on Development 167 



to time as the experiments required. In discussing the experi- 

 ments the percentage solutions are expressed in gram-molecular 

 terms. The sugar solutions were prepared fresh for each experi- 

 ment since they soon became acid with a fungus-like grewthif kept 

 for any length of time. Cane sugar inverts to some extent in solu- 

 tions and may thus vitiate the calculations for osmotic pressures. 

 It was found that the amount of solution and the number of 

 eggs in the bowl affected to a greater or less degree the rate of 

 development. A large number of eggs in a bowl almost full of 

 liquid develop more slowly than fewer eggs in less liquid; this is due 

 to a difference in oxygen supply as will be shown below. In the 

 same experiment, therefore, approximately equal numbers of eggs 

 and equal amounts of liquid were placed in each bowl. Since 

 there is some individual variation in the eggs from different females 

 the experiment and control were as far as possible from the same 

 batch of eggs. 



PERMEABILITY OF THE EGG MEMBRANES 



A recent paper by Brown ('05), questioning the permeability 

 of the egg membrane of Fundulus necessitates a discussion of this 

 subject. The solution of this question is also essential in order to 

 properly interpret my experiments. 



Loeb in 1893 showed that diffusion through the egg membrane 

 of older embryos occurred very readily. The addition of 3 grams 

 of KCl to 100 cc. of sea-water brought the heart of a Fundulus 

 heteroclitus embryo to a standstill in a few minutes. A consider- 

 able amount of the salt must, therefore, diffuse through the egg 

 membrane in a very short time. I repeated this experiment in 

 the following manner: Seven five-day embryos were placed in a 

 0.67 m (about 5 per cent) solution of KCl. Within ten minutes the 

 heart action of one had ceased, another stopped in eleven minutes, 

 and three others in twelve minutes. The heart's action becomes 

 first periodic and jerky and then gradually stops, though it will 

 often continue to give weak irregular contractions at intervals of 

 one or two minutes for some time after it has apparently stopped. 

 The embryos began to wriggle after having been in the solution 

 only three or four minutes. When the hearts of all the individuals 



