1896.] Embryology. i 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 König, 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 MgCl, 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 obtainedjthe 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 Hin into account in connection with the time periods 
given. 
The first furrow appears at the superior pole without any previous 
flattening asin Amblystoma (Eycleshymer, Jour. of Morph., X, p. 348). 
At first it is a shallow groove just at the pole itself, but it soon spreads 
