1896.] 



Embryology. 



763 



O. Hertwig and Schultze have recently experimented on the influence 

 of a very low temperature upon the development of the eggs of Rana 

 fusca with very different results. 



Hertwig (Sitzungsberichte der Konig, Preuss. Akad. d. Wiss, 5 April, 

 1894, p. 313) found that freshly fertilized eggs were injured by an ex- 

 posure to a temperature of 0° C. for 24 hours. On being raised to the 

 ordinary temperature a portion were developed very much more slowly 

 than normal eggs, -while in the remainder a part of the yolk was found 

 incapable of division. 



Schultze (Anatomischer Anzeiger, X Band, No. 9) subjected eggs of 

 the same species to a temperature of 0° C. for 14 days, and then ob- 

 tained perfectly normal embryos from them. These eggs had reached 

 later stages of development before being cooled, and he does not state 

 whether their subsequent development was more or less rapid than 

 ordinary. 



Subjection to a temperature of 0° C. for so long a period would proba- 

 bly have a very different effect from that of only a few hours duration. 



Loeb and Norman (Archiv. f. Entwick, III Band, No. 1), experi- 

 menting on the eggs of the sea-urchin, Arbacia, found that when put in 

 sea water to which had been added 2-3 per cent. NaCl or MgClj seg- 

 mentation of the protoplasm was wholly prevented, but that the nucleus 

 went on dividing. On being put into normal sea water after a few 

 hours exposure to the concentrated solution the eggs divided at once 

 into several cells, the protoplasm merely rearranging itself around the 

 new nuclear centers. 



Possibly the same may be true in these frog's eggs when subjected 

 for a short time to a freezing temperature, and the subsequent hasten- 

 ing of segmentation may be due to the fact that the nucleus has already 

 divided. 



In watching the segmentation of these eggs the great (comparative) 

 size and depth of the furrows was specially noticed, together with the 

 distinctness of the wrinkles formed along either side of them. 



Accordingly it was determined to study their segmentation more in 

 detail, and a fresh lot was obtained]the next morning. These remained 

 in ice water only one hour, just long enough to get them home. They 

 were then transferred to watch-glasses and examined in strong sunlight. 

 This fact must be taken into account in connection with the time periods 

 given. 



The first furrow appears at the superior pole without any previous 

 flattening as in Amblystoma (Eycleshymer, Jour, of Morph., X, p. 348). 

 At first it is a shallow groove just at the pole itself, but it soon spreads 



