•AG 



lilt' inotlicf, and posscssiiio- a jelly layci-, were exposed to 

 -4° I'or 1 hoiii- and ihrii arl ilicially fei-tilized and placed 

 in favorable conditions for development. In the first 

 hours after tliawint;-, no externally perceptible chang-es in- 

 dicative of fertilization conld be observed, hnt 14 honrs 

 after fertilization, the cleavage process commenced and 

 thereafter ])roceeded at the normal rate. 



P^ischer-Sigwart {Vlerteljahrscli. d. Naturf, Ges. Zurich, 

 62, 1897) records finding- masses of frog eggs which had 

 been frozen solid for 2 days, during which time the tem- 

 perature sank to -8°. When the eggs were gi'adually 

 thawed ont, they underwent a normal process of develop- 

 ment, though this was somewhat slower than usual. 



Pictet (1893) says that he cooled frog eggs to -60° for 

 several hours and that they developed into tadpoles. 



Several investigations are found in the older literature 

 on the death point of bird eggs, but many authors over- 

 looked the fact that it takes a relatively long time for the 

 interior of the larger eggs to reach the equilibrium of 

 temperature with the surrounding atmosphere. There 

 thus result some apparent contradictions which partially 

 vanish when one considers the temperature of the hath or 

 of the atmosphere in the various experiments, the time of 

 exposure, the size of the eggs and the other factors which 

 determine heat conduction. A short review of some of 

 the literature will be found in Moran (1925). We shall 

 describe here a few of the more typical investigations on 

 chicken eggs. 



Lipschiitz and Illanes (1929) reported that of 33 lien's 

 eggs, exposed for 3 to 7 hours to an air temperature of 



- 4° to - 6°, 20 developed embryos or yielded chicks, these 

 latter retaining their normal appearance throughout an 

 observation period of several months. In another series 

 of experiments, the temperature within the eggs was de- 

 termined by inserting a thermometer into a hole in the 

 egg. Temperatures of - 2.5° to - 4.5° were thus recorded. 



Rabaud (1899) put to freeze in an ice-salt mixture at 



- 18°, 30 sets of 18 eggs each. He left them in the mixture 



