132 CHARLES R. STOCKARD 



Lot Cs contained 10 unhatched, one of which was abnormal, the 

 others were all normal. 



Lot Di, only one unhatched, all seem fine. 



Lot D2 contained 2 unhatched, and lot D3 had 3 unhatched, though 

 all of these seemed normal. 



This experiment shows very clearly that stopping or arrest- 

 ing the development of Fundulus eggs after about twenty-four 

 hours of development, when gastrulation has definitely begun, 

 produces very slight or no ill effects on such specimens up to 

 the time of hatching and becoming free swimming little fish. 

 Whether during later stages of growth these fish might show some 

 disadvantages following the developmental interruption we have 

 not attempted to determine. It is probable, however, that these 

 specimens were interrupted in their development during a particu- 

 larly passive period and that no later disadvantages would 

 accrue. This would seem further probable since it is at just such 

 a stage in development that the eggs of birds are normally inter- 

 rupted, and clearly wdthout ill effects on the group. 



These experiments not only show that stopping development at 

 this stage, just after gastrulation has started, is not noticeably 

 injurious in effect on the development of the young fish, but 

 further, that after gastrulation has commenced the rate of devel- 

 opment of the embryo may be slowed to a most extreme degree, as 

 occurred in the upper temperatures of the refrigerator, without 

 serious injury to the structure of the young fish. 



To further establish the correctness of the above results, we 

 may record one other similar experiment in brief detail. 



Experiment 906. 64.1. A group of eggs when 24 hours old containing 

 all normal fine specimens were placed at a temperature of 5°C., and 

 later compared with a selected control from the same parents. 



At 46 hours old, the control were developing rapidly, with the germ- 

 rings almost completely over the yolk and the embryos well formed. 



The B4.2 lot now in cold for 22 hours showed the same condition as 

 when placed in the refrigerator except that the segmentation cavities 

 were distended so that a vesicle appeared below each disc. These 

 eggs were now moved to an upper compartment of the refrigerator to 

 allow them to develop slowly at a temperature of about 9°C. 



When four days old in the 9°C. temperature they were developing 

 slowly but normally, with the germ-rings about one-half over the 

 yolk-spheres and with embryonic shields in which the axis of the 

 embryo was beginning to form. 



