PAR THENOGENESIS 



genetic development of the sea-urchin's q^^^ by means of 

 butyric acid and hypertonic sea-water, the butyric acid is 

 equally efficient in action preceding or following the treat- 

 ment with hypertonic sea-water. This notable difference 

 between "chemical fertilization" and nature's process the 

 theory discounts. Though Loeb was the first to know that 

 the order of treatment could be reversed, he made no 

 attempt to explain this difference from the natural process. 



Sharply visible ectoplasmic changes are always pres- 

 ent in fertilization but not in all cases of experimental 

 parthenogenesis. As we have seen above, the eggs of sea- 

 urchins develop with Loeb's original hypertonic sea-water 

 method, although without membrane-separation. The 

 double treatment is not essential.^ 



Because of these considerations we must flatly dismiss the 

 superficial cytolysis-corrective factor theory as an attempt 

 to explain fertilization as we have dismissed it as an explana- 

 tion of experimental parthenogenesis; it fails not only for 

 eggs generally but also for sea-urchins' eggs specifically. 



But the fact remains that parthenogenesis can be experi- 

 mentally induced. What is experimental parthenogenesis ? 



If terms mean anything, we should expect that in experi- 

 mental parthenogenesis, as in natural, perfect and complete 

 development should result. Yet, as we have seen, generally 

 experimental parthenogenetic development does not extend 

 beyond the larval stage. This is undoubtedly often due to 

 our failures to overcome the difficulty of rearing animals to 

 the adult stage from eggs under laboratory conditions. - 

 Some difficulty also inheres in the methods employed: 

 means of experimental parthenogenesis often tend to do 



^ It is curious that Loeb insisted that the superficial cytolysis factor 

 is the essential one; he thereby denied his own discovery and deprived 

 himself of all ground in his whole fight concer?iing priority. 



^ I have been able to carry Platynereis megalops through three 

 generations under laboratorx conditions. 



235 



