176 CHARLES R. STOCKARD 



located specimens were small and far behind the control in their rate 

 of development, but here only about 10 per cent of them were actu- 

 ally grossly deformed, and there were no double conditions at all. 



The second group in boiled sea-water was more decidedly affected 

 than any. Man}^ of the eggs died. Many superficial ones were 

 almost up to the control in their state of development. But the great 

 majority of specimens were small, pale, and poorly developed, being 

 several days behind the control. Almost 16 per cent of these small 

 specimens were considered to show gross defects. Twelve specimens 

 had no circulation of the blood; 10 had decidedly defective eyes, minute 

 in size and poorly developed or deeply buried in the head, and two 

 were cyclopean. 



Four specimens that were near the surface of the clusters and very 

 well developed presented double conditions. One egg contained sepa- 

 rate twins, both embryos being fully developed. The 3 other eggs 

 showed different degrees of anterior duplicity. Therefore, more than 

 2 per cent of the entire number of specimens developing in the dish 

 were double; this is much the highest record that was obtained among 

 ten similar experiments. 



The other experiments with low oxygen supply gave closely 

 comparable results to the three above, and need not be reviewed 

 in detail. Only a very small number of double specimens oc- 

 curred in any of them. In all cases, the double individuals were 

 among those of fairly normal development and were not extremely 

 small and highly defective specimens. This, in my opinion, is 

 a fact of considerable importance, and is to be explained some- 

 what as follo\vs. 



The origin of two embryonic axes or growing points on the 

 germ-ring of the fish probably results from a rather mild or 

 slight reduction in the normal developmental rate at the time of 

 gastrulation or embryonic-shield formation. It is probably more 

 important to obtain the reduction in rate at an exact and very 

 limited moment than to have a definite degree of reduction. 

 That is, the reduction in rate may be little or much, but it must 

 occur during a very limited time and not continue for long after 

 the doubling has once been accomplished. Should the arrest 

 continue, it is possible that one of the buds, even though it had 

 begun to develop, might be suppressed, and the more vigorous 

 or more favorably placed one might later continue as an appar- 

 ently single individual. 



