40 THE PHYSICAL BASIS OF LIFE 



sions of ail underlying more fuiidameiital organization 

 that escapes the eye ; but it is precisely this organization 

 of which we are ignorant. Experiment has shown in one 

 case at least (the eggs of nemertines) that fragments 

 from eggs taken prior to the period of visible localization 

 develop as miniature wholes, — a fact which points unmis- 

 takably to the conclusion that the fundamental pattern of 

 localization has not yet been established in the ooplasm at 

 that time. It has thus been made probable that even the 

 most general features of the organism, perhaps even such 

 fundamental ones as polarity and bilaterality, are not 

 present at the beginning but like other characters are es- 

 tablished in the egg by a process of epigenesis.^^ 



The point of especial interest to the cytologist is the 

 fact that the visible patterns in the ooplasm produced by 

 configurations of the various formed bodies do not consti- 

 tute its fundamental organization but are only an out- 

 ward sign or index of that organization. For in the first 

 place (as has just been shown), these patterns are absent 

 in the earliest stages, being produced subsequently by 

 processes of development. In the second place, as demon- 

 strated by the experiments of Lyon, Morgan, Lillie, Conk- 

 lin and others, the visible patterns may in many cases be 

 disturbed or even almost obliterated by subjecting the egg 

 to a strong centrifugal force (by which the formed ])odies 

 are displaced) without destroying the capacity for later 

 normal development, and often without even serious tem- 

 porary impairment. Once more, therefore, we are driven 

 to the conclusion that tJie primary basis of the egg-organi- 

 zation lies in the ground-siib stance or hgaloplasm; and 

 that it is primarily the components of this system that are 

 sifted apart and distributed during the cleavage of the 

 egg according to a perfectly definite order. The visible 



