STRUCTURE AND DEVELOPMENTAL RATE 135 



When 22 days old, the Eo group contained 25 hatched and 20 un- 

 hatched. Three of the latter were abnormal with no blood circulation, 

 two being small and inactive, and the third was grossly deformed. 

 The E3 group had 25 hatched and 11 unhatched, all of which seemed 

 normal in structure. 



At 25 days old, 4 of the Eo group were still unhatched, but all of 

 the E3 lot had hatched. They were kept until 34 days old, at which 

 time many had died on account of the difficulty in feeding them, but 

 the 4 specimens in lot E2 never succeeded in hatching. 



When these records of late arrests are compared with those 

 from eggs arrested during early cleavage stages, one will be struck 

 with the low mortality following removal from the refrigerator in 

 the case of the former. The complete absence of double monsters, 

 ophthalmic deformities, etc., among the specimens arrested dur- 

 ing late stages also contrasts with the common occurrence of such 

 conditions among specimens arrested during cleavage stages. 

 The general nature of the circulatory disturbances, etc., which do 

 occur after late arrests is also characteristic. A contrast is 

 further noted by considering this experiment in comparison with 

 the specimens described above which were introduced into the 

 cold after one day of development — there again the advantage in 

 subsequent development is on the side of those specimens caused 

 to develop very slowly during the later developmental stages. 

 But of the specimens almost completely stopped in development, 

 those stopped very soon after gastrulation seem to have an ad- 

 vantage over specimens stopped when one day older, or further 

 advanced in development. The stage immediately following the 

 first rapid changes of gastrulation would seem to be an extremely 

 indifferent period. 



Two other sample experiments will be reviewed in brief to 

 illustrate the gross reaction following still later developmental 

 interruptions. It must be realized that in all of these experi- 

 ments we are at present sunply recording the outward gross 

 appearance and behavior of the specimens. A closer microscopic 

 examination of the young fish in section might show a consider- 

 able depression in the development or expression of certain inter- 

 nal organs, for example, the conditions in the branchial regions, 

 digestive glands, etc., while observation of the living specimen 

 had given no indication of its inner defective condition. 



