310 STUDIES IN GENERAL PHYSIOLOGY 



opment of the embryo. The details are given in the fol- 

 lowing pages. 



I. THE RELATIVE SENSITIVENESS OF THE EMBRYO TO LACK 



OF OXYGEN 



1. The fact that embryonal development soon stops, and 

 that the embryo dies without oxygen, has been shown to be 

 true so often by experiment that it is not necessary to discuss 

 it here. 1 I tried to determine, first of all, how long and how 

 far development could go in various stages of development 

 at the same degree of lack of oxygen; and, secondly, how 

 long the embryo could remain exposed to the same degree of 

 lack of oxygen in different stages of development without 

 losing its power of development. The stages of development 

 which were studied were the following : (1) the freshly fer- 

 tilized egg; (2) the egg after the formation of the blasto- 

 derm, but before the formation of the embryo, about twenty- 

 four hours after fertilization ; (3) the egg after the beginning 

 of the formation of the embryo, about forty-eight hours 

 after fertilization (the embryo usually had at this time optic 

 vesicles in which the lens was just being formed) ; (4) the 

 embryo just after the circulation was established, seventy- 

 two hours after fertilization ; and finally various later stages. 

 The egg of Fundulus is especially well adapted to these ex- 

 periments, because it is very tough, develops fully in the 

 aquarium, and the fish hatches in the aquarium. The 

 entire period of development takes in summer, at a tempera- 

 ture of about 24 C., about twelve to fourteen days. 



The method used in these experiments was similar to that 

 of Bunge in his well-known experiments on the need of 

 oxygen in lower animals. a About 6 c.c. of potassium hy- 

 droxide and pyrogallol are put into a test-tube (according to 

 Hempel's directions). Into this test-tube is introduced a 



1 For the literature on this subject see DttsiNG, PflUgers Archiv, Vol. XXXIII. 



2 BUNGE, Zeitschrift fiir physiologische Chemie, Vol. XIV, p. 322. 



