THE BIOLOGY OF THE CELL SURFACE 



rapidity with which unfertilized eggs separate fully their 

 membranes while in distilled water; by the rate at which 

 fertilized eggs form extra-ovates when in hypotonic sea- 

 water; and by the failure of heavily inseminated eggs 

 to show polyspermy. Whenever these initial reactions are 

 qualitatively poor, the development of the eggs is below 

 normal.^ These criteria I find hold for three other species 

 of sea-urchins at Naples.- Also, for the egg of Nereis the 

 quality of the striking ectoplasmic changes subsequent to 

 fertilization constitutes an index of the condition of the 

 egg and the quality of its later development.^ 



Further I found criteria which in later stages of develop- 

 ment indicate whether this will be normal in its whole 

 course. For example, in eggs of Nereis and Platynereis, 

 the behavior of the oil drops is a reliable index of normality; 

 one may be sure that swimming forms which possess one 

 oil-drop and only one in each of the four gut cells can 

 develop through metamorphosis to the adult stage and 

 that no other will.^ Doubtless other criteria can be found 

 for every stage of the development. Every one such will 

 prove valuable in extending our knowledge as to what is a 

 good egg. In all cases however, where such criteria are not 

 known, the whole course of development must be always 

 followed before it can be said that development is normal. 



It is clear that the condition of eggs largely depends 

 upon that of the animals from which they come. Eggs 

 normally shed from animals in a good state are preferable 

 to those shed by weak animals and by^ animals in abnor- 

 mal conditions. In every experiment comparison with 

 and control by the normal, untreated cell or organism 

 is obviously absolutely necessary. The quality of the 



^ Just, ip28c. 

 - Just, ig2gc. 

 •' Just, 1915a. 



4 Just, I922g. 



24 



