The Influence of External Factors on Development I'jl 



healthy condition without the embryos breaking through the 

 membranes. Thus these fish remained enclosed in their egg 

 membrane for thirty-three days while the control had begun to 

 hatch after thirteen days. 



As there are some points of interest to be brought out in con- 

 nection with the details of this experiment it may be briefly 

 described. Eggs were placed, shortly after fertilization, on moist 

 glass with all superfluous water removed, they were arranged so as 

 not to be in contact with one another and then covered with a finger 

 bowl to prevent the evaporation of the surrounding moisture. 

 Other eggs were arranged in a similar manner when in the two-cell 

 stage, while still others at this period were covered by finger bowls 

 which had moist filter paper closely pressed in them, thus insuring 

 a more moist atmosphere about the eggs. 



When the eggs were fifty-three hours old the control in sea- 

 water showed embryos distinctly formed with the blastopores 

 closed, those on the moist glass also had their blastopores closed 

 and were slightly in advance of the control in their development. 

 One of the eggs that had become dried and shrunken also showed 

 a normal embryo. At three, four, six and ten days old the ones on 

 the moist glass were continuing to develop normally though at a 

 faster rate than the control. This more rapid development was in 

 all probability due to the better aeration out of water. 



When fourteen days old many of the control had hatched. At 

 this time those that were under finger bowls without moist paper 

 had become so dry, although moisture had been added several 

 times, that a number of them died; in one lot fifty-four were dead 

 and only twenty still alive, while another lot had forty-seven living 

 and thirty-four dead. This and other such cases indicate that it is 

 important to keep the eggs moist. The ones supplied with moist 

 filter paper were all alive. None of these eggs out of water had 

 hatched; twenty-three were then taken from the glass plate and 

 put into a finger bowl containing sea-water. Eleven hatched; in 

 five minutes, eighteen were out after ten minutes and the entire lot, 

 twenty-three, were swimming about after being in the sea-water 

 for only eighteen minutes. These fish after hatching seemed 

 further developed than the controls which had also hatched, evi- 



