LOW TEMPERATURE — DEVELOPMENT OF FUNDULUS 451 



materially affect the oxygenation of the eggs is sufficiently in- 

 dicated by the normal development of similarly handled con- 

 trols in the room temperature. The possible effect of dark- 

 ness in the refrigerator was controlled in only one instance, 

 when no effects were observed. 



If the temperatures used be not too low (11-13°C.) the only 

 marked immediate effect seems to be the retardation of normal 

 development, which is resumed at its usual rate when the ova are 

 returned to the ordinary temperatures of the laboratory (20- 

 24°C.). It is a simple matter thus to prolong the age of the 

 early blastula from the normal average of about five hours, to 

 more than two weeks, that is some sixty-five times, and prob- 

 ably it might be prolonged much more. Such blastulas, re- 

 placed in the room, may develop and hatch quite normally, or 

 they may form embryos showing marked abnormalities, indi- 

 cating that underlying their normal appearance earlier there was 

 an actual disturbance of some kind. One can not. always say 

 by superficially inspecting the entire blastula, or later stage, 

 whether it is completely normal or not. 



Subjection to a lower temperature (8-10°C.) for a few hours 

 or days, is usually followed either by death or by abnormal 

 development, normal development after such treatment being 

 found in only a small percentage of the total treated. It should 

 be noted, however, as a point of some importance, that in every 

 experiment where development continued at all, after removal 

 from the refrigerator, at least a small percentage of the embryos 

 developed normally. 



Considerable variation was observed among different lots of 

 eggs, some showing few abnormalities after a treatment that re- 

 sulted in very few normally hatching larvae from other lots of 

 eggs. It should also be noted that in one, and in only one, con- 

 trol, did the total proportion of abnormal embryos equal the 

 minimum observed after subjection to a low temperature for 

 more than five hours ; and in no other case did the abnormalities 

 in the control even approach the minimum in treated lots. 



Eggs placed in the refrigerator within two to five minutes after 

 insemination usually proceed to form a germ-disc which differs 



