MORTALITY OF THE COD EGG IN RELATION TO TEMPERATURE

¹ From the Biological Laboratories, Harvard University, Cambridge, Massachusetts

1. Experiments were carried out at four different temperatures in the supra-optimal range of development for the cod egg.

2. Development from the two-cell stage to 50 per cent hatched required 8.5 days at 12° C., 9 days at 10° C., 11.5 days at 8° C., and 17.2 days at 6° C.

3. At all temperatures an initial period of high mortality decreased with the closing of the blastopore and was followed by a period of low mortality until the embryo was three-quarters the circumference of the egg membranes, when the mortality steadily increased up to hatching.

4. The hatching period is discussed with reference to its use as a stage of development.