XI 



ON THE RELATIVE SENSITIVENESS OF FISH EMBRYOS 

 IN VARIOUS STAGES OF DEVELOPMENT TO LACK 

 OF OXYGEN AND LOSS OF WATER 1 



IT is probable that the series of successive changes in 

 form which we call the development of an animal embryo is 

 accompanied by a corresponding series of physiological 

 changes. While we are well acquainted with the changes in 

 form, so far as their mere morphology is concerned, we know 

 but little concerning the changes in the physiological reac- 

 tions of the embryo in its various stages of development. 

 It is a well-known fact that the embryo has a greater vital- 

 ity than the completely developed animals. 2 Systematic 

 investigations, however, are lacking as to whether this vital- 

 ity decreases steadily with the progress of the development 

 of the embryo, and as to whether this decrease is the same 

 toward different variables. In order to obtain an answer to 

 these questions, I studied the relative sensitiveness of the 

 fish embryo (Fundulus) to lack of oxygen and loss of water 

 in different stages of its development. I found in general 

 that the embryo is the more sensitive to lack of oxygen, the 

 older it is. Yet the sensitiveness increases more rapidly at 

 first than later. On the other hand, the experiments on the 

 effect of withdrawal of water gave a totally different result. 

 The germ of the embryo is much more sensitive to loss of 

 water in the first stages of its development (during cleavage 

 and before the beginning of the formation of the embryo 

 proper) than after the formation of the blastoderm, and 

 its sensitiveness decreases with the increase in the devel- 



1 Pflilgers Archiv, Vol. LV (1894), p. 530. 



2 ZUNTZ, Pfliigers Archiv, Vol. XIV ; and PFLttGEK, ibid. 



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