THE BIOLOGY OF THE CELL SURFACE 



too much — though they initiate development, they also 

 impair it. 



Even if we in time overcome these difficulties, there 

 still remains doubt that the action of the means of induced 

 parthenogenesis is identical to that of the spermatozoon. 

 For while normal, fertilized eggs do, if properly handled, 

 give at least 95 per cent, perfect larvae, it is difficult if not 

 impossible to obtain this percentage in experimental par- 

 thenogenesis. The spermatozoon is more effective than 

 a means of experimental parthenogenesis; frequently one 

 finds that a certain lot of eggs, a sample of which will give 

 more than 95 per cent, fertilization and perfect develop- 

 ment, will not respond to a means of parthenogenesis that 

 is usually effective on eggs of this species. 



On more general grounds it is still to be doubted that an 

 experimental means duplicates the action of the normal 

 stimuli in the intact organism, though experimental 

 imitation is often possible. Despite these considerations 

 however, it must be clearly emphasized that complete 

 development can be induced experimentally. 



Even if we do not yet succeed in establishing the par- 

 ticular way in which either spermatozoa or experimental 

 means act upon the egg so that it develops, we certainly 

 can agree that either spermatozoon or experimental means 

 in initiating the development of the egg produce the same 

 result — a succession or rhythm of mitoses and cleavages 

 which finally lead to embryo-formation. As we have 

 already seen, the experimental means are not specific. 

 Most probably, the nature of the reaction between experi- 

 mental means and egg differs also from that between sper- 

 matozoon and egg, since there is evidence to indicate that 

 fertilization is a chemical union of an egg-substance with 

 the spermatozoon, whereas we can assume that the initial 

 action of the experimental means is physical. But the 

 end-result, however reached, is the same. The conclusion 



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