The Influence of External Factors on Development 173 



as an eighteen day control embryo which had been free swimming 

 for four or five days. 



When twenty-seven days old, more embryos were dying, but 

 those put into sea-water began to hatch within ten minutes, though 

 they swam abnormally at first, going in a circular or spiral course. 

 This was due to the fact that the fish had become cramped by 

 its twisted position within the egg membrane and for an hour or so 

 after hatching they were unable to straighten themselves, but they 

 finally do so and their movements become normal. When at rest 

 the crooked ones have a tendency to topple over on one side. 



Fig. I. A normal embryo just hatched, twelve days after fertilization, yk, yolk mass. X17 

 diameters. 



Fig. 2 A newly hatched embryo which was developed out of water and made to hatch by being 

 placed in sea-water when eighteen days old. yk, yolk mass. X 17 diameters. 



After thirty-one days they were still well and unhatched on the 

 glass although a few had starved to death each day. When thirty- 

 two days old, five were placed in sea-water, three came out within 

 twelve minutes and all were out in twenty-three minutes after 

 being put into the water. These had their bodies bent owing to 

 the long cramped position they occupied withm the egg membrane, 

 though all soon straightened out and swam normally. 



