FACTORS IN ONTOGENY 



281 



of the egg is not limited by its prospective fate. If accident 

 in nature or ruthless handling in the experimenter's labora- 

 tory destroy or remove part of the egg, the remainder has a 

 power of regulation which is in some respects the highest 

 and most important kind of organic adaptation that we know. 



The same data derived from the 

 experimental study of development, to- 

 gether with data got from the experi- 

 mental study of mature and even 

 senescent stages of various organisms, 

 constitute our chief evidence touching 

 the problem of mechanism versus vi- 

 talism. This problem may be posed in 

 question form as follows: In how far 

 can so-called vital phenomena be ana- 

 lyzed into physicochemical, or mechan- 

 ical phenomena? Is life simply an in- 

 teraction, very complex to be sure, and 

 so far largely unanalyzed and hence not 

 directly referable to specific physico- 

 chemical causes, between substances of 

 particular chemical and physical struc- 

 ture and those familiar forms of energy 

 known to us in the physicochemical 

 world, or is it the result or manifestation 

 of an extra physicochemical force and 

 set of conditions? 



When the sunflower bends its face 

 always toward the sun, we do not at- 

 tribute this behavior either to the in- 

 telligence or the instinct of the plant. 

 But when young spiderlings or moth 

 caterpillars or green aphids just from 

 the egg move with one accord toward 

 the light side of the glass jar, we do attribute this behavior to 

 animal instinct or to the exercise of a preference or choice. 

 When iron filings rush toward a magnet brought sufficiently 

 near them, we have on our tongues' end the sufficient explana- 

 tion of this behavior in the single word "magnetism." Now 

 the biological mechanist, observing that in all these cases 

 there is a certain apparent definite relation between a cause 



FIG. 163. Extra - ovates 

 from the eggs of the sea 

 urchin, Arbacia. By di- 

 luting the sea water the 

 osmotic pressure bursts 

 the egg membranes so 

 that part of the egg plasm 

 issues and forms an ex- 

 tra-ovate. (After Loeb.) 



