158 CHARLES R. STOCKARD 



and resumed a normal rate of development. Such a procedure 

 introduced at this given developmental stage seemed to have no 

 effect other than to throw the lot of. eggs several days behind the 

 control in their degree of development and time of hatching. 



In order to determine the ability of the embryo to initiate 

 certain functional reactions when developing at an extremely 

 gradual rate, specimens three days old, just prior to the establish- 

 ment of a heart beat, were placed in the refrigerator at 5° and 8°C. 

 These temperatures do not seem to inhibit changes in the late 

 embryo to the same extent as they do the early cleavage processes. 

 The group in 5°C. still had no heart beat after being chilled for 

 five days, so these specimens may be said to have been almost 

 completely stopped. After five days the lot at 8°C., however, 

 had developed a very slow and feeble heart beat. Thus these 

 had definitely progressed at such a temperature and had estab- 

 lished the functional activity of the heart muscle. Both groups 

 on being returned to room temperature recovered completely 

 and hatched in a normal fashion. Therefore, neither stopping 

 for five days nor slowing to an extreme degree the development 

 of these three-day-old embryos produces noticeable effects on 

 their subsequent development and hatching ability. 



If abnormal development is simply the result of developmental 

 arrests, why should not eggs which have been decidedly slowed 

 in their developmental rates by lowering their temperature give 

 rise to monsters as frequently as do those eggs which have been 

 actually stopped in development at critical stages? When eggs 

 are treated with alcohol, other anaesthetics, or a great variety of 

 chemical substances, their development is not necessarily entirely 

 stopped in order to induce monstrous results. These specimens, 

 however, act during later development in a manner much more 

 comparable to that shown by eggs actually stopped by refriger- 

 ation than like specimens in which the developmental rate was 

 simply greatly reduced. The explanation of this fact is probably 

 as follows: 



Specimens which are caused to proceed at a greatly reduced 

 though continuous rate of development by simply lowering their 

 temperature apparently adjust the developmental progress of 



