CHAPTER X 



Artificial Parthenogenesis 



IN addition to the naturally occurring parthenogenesis 

 which, as has been seen in the preceding chapter, is 

 widespread in the animal kingdom, there is another type of 

 parthenogenesis that has attracted much attention in 

 recent years. It has long been known that certain animals, 

 for example the common silk-worm, occasionally lay eggs 

 which may develop without fertilisation although they are 

 not normally parthenogenetic, and that this occurs more 

 readilyif the eggs have been shaken or treated with acid. The 

 matter attracted little attention, however, until J. LOEB 

 undertook experiments with the eggs of Sea-urchins, and 

 found that by various methods of treatment he could cause 

 them to develop without fertilisation. It is not proposed 

 here to enter upon a full history of the earlier experiments 

 and the hypotheses that were put forward to account for 

 their results, nor to consider in detail the very complicated 

 physico-chemical problems raised, but rather to give a 

 general account of the results obtained and their bearing 

 on cytological study. 



It has been found possible to cause parthenogenetic 

 development of Sea-urchin eggs by very various methods of 

 treatment. One of the earliest was by the addition of various 

 mineral salts, such as magnesium chloride, to the sea-water, 

 but since many salts were effective it was not possible to 

 ascribe the initiation of development to the chemical action 

 of specific substances ; it seemed rather to be caused by the 



