iS6 ANIMAL AGGREGATIONS 



The retarding effects of secretions of growing embryos are removed in 

 the presence of animal charcoal and fuller's earth. The percentage of 

 normal larvae resulting from eggs grown in the presence of these 

 adsorbents is greatly increased, while mortality is decreased." 



By using hanging-drop cultures, a part of which contained isolated 

 sea-urchin eggs while the others held small groups of eggs, Frank and 

 Kurepina (1930) report accelerated growth in the grouped eggs. 

 These results are particularly noticeable if the temperature is al- 

 lowed to rise slightly above the normal. A resume of two of their 



TABLE VII 

 A 



Number of eggs per drop 1-2 16-20 



Number of such drops ^ . . lo 3 



8| hours after fertiUzation 75% have 8 blasto- o % at 8 blastomeres 



meres 12% past 8 blasto- 

 25% past 8 blasto- meres 



meres 88% at 16 blastomeres 



B 



Number of eggs per drop 1-2 



Number of such drops 10 



42:1 hours after fertiliza- 

 tion /S*: no movement 



25% slight move- 

 ment 

 10% plainly mov- 

 ing 

 0% gastrulae* 



* Percentages as reported in original work. 



experiments, showing the type of results obtained under these con- 

 ditions, is given in Table VII. These results are interpreted by the 

 experimenters to indicate a stimulating effect of self-radiation as 

 suggested by Gurwitsch's mitogenetic rays. It is clear that such an 

 interpretation is far-fetched at present; but the results indicate, 

 despite careless reporting, that there is an optimum number of eggs 

 which lies well above the minimum at which, under certain condi- 

 tions at least, growth is favored as compared with that shown by 

 eggs isolated into similar amounts of sea-water. 



