32 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



genesis," that is to say, the possibility of development without 

 fertilisation, since owing to the brilliant discoveries of the 

 American physiologist, Jacques Loeb, this topic forms one 

 of the centres of biological interest at present. It has long 

 been known that the eggs of certain bees, lice, crayfishes, 

 and other animals and also plants, are capable of develop- 

 ment without fertilisation at all. Now Eichard Hertwi" 



o 



and T. H. Morgan already had shown, that at least nuclear 

 division may occur in the eggs of other forms in the egg of 

 the sea-urchin for instance when these eggs are exposed to 

 some chemical injuries. But Loeb l succeeded in obtaining 

 a full development by treating the eggs of echinoderms with 

 chloride of magnesium ; thus artificial parthenogenesis had 

 been discovered. Later researches have shown that artificial 

 parthenogenesis may occur in all classes of the animal 

 kingdom and may be provoked by all sorts of chemical or 

 physical means. We do not know at present in what the 

 proper stimulus consists that must be supposed here to> 

 take the place of fertilisation ; it seems, of course, highly 

 probable that it is always the same in the last resort. 2 



But enough about processes, which at present are of a 

 highly scientific, but hardly of any philosophic interest. 



By fertilisation propel we understand the joining of the 

 male element, the spermatozoon or the spermia, with the 

 female element, the egg. Like the egg, the spermatozoon is 

 but a cell, though the two differ very much from one another 



1 Amer. Journ. PhysioL vols. iii. and iv. 1900. 



2 According to Delage (Arch. Zool. exp., 3 ser. 10, 1902), it is indifferent 

 for the realisation of artificial parthenogenesis, whether but one, or both, or 

 neither of the "polar bodies " has been formed. But the egg must be in the 

 first stages of maturation to the extent that the " nuclear membrane " must 

 be already dissolved. 



