436 SCIENCE PROGRESS 



ments are, however, open to criticism, as later work has shown 

 that a small proportion of unfertilised silkworm eggs will 

 develop parthenogenetically without the use of stimulating 

 agents. 



Our first real knowledge of artificial parthenogenesis we 

 owe to Loeb, Delage, Bataillon, Lillie, and many others, who 

 worked in the first place with Echinoderm and Frog eggs. 



We now know that the phenomenon can occur in animals 

 widely separated, as, for example, Insects, Echinoderms, 

 Mollusca, Amphibia, to mention only a few cases. Further, the 

 methods which can be employed are very varied, the chief 

 ones being : 



(i) Hypotonic solutions (distilled water). 



(2) Nearly isotonic solutions made by adding to sea-water 



or to distilled water the following substances : acids, 

 alkalies, neutral salts. 



(3) Hypertonic solutions made by the addition of the above 



mentioned substances. 



(4) Mechanical shocks, thermal changes, fat solvents, alka- 



loids, blood sera, bile salts, etc. 



(5) Electrical shocks by induction coils. 



These various agents are not effective on all species of eggs, 

 indeed, some are only of use for one particular species. It is 

 one of the problems of the future to ascertain whether there 

 is to all the methods a common factor capable of initiating 

 the development of unfertilised eggs ; until this is done it is 

 impossible to decide what action the sperm has at fertilisation 

 causing the complicated series of evolutionary changes culmi- 

 nating in the adult animal. 



For such reasons it is impossible to accept the complicated 

 and highly problematical physico-chemical explanations given 

 by Loeb ^ and others. 



The discovery of artificial parthenogenesis is, however, of 

 great importance in demonstrating that many, if not all eggs, 

 are capable of development without the co-operation of the 

 male element, provided that suitable means are adopted to 

 effect this result. In the past it was assumed that the egg was 

 an inert protoplasmic mass incapable of performing its functions 

 unless it were revivified and changed by the spermatozoa. 

 The truer conception appears to be that the egg has an evolu- 

 tionary course before it leading to the adult animal, and that 

 the sperm or artificial agents simply direct this course without 

 in any way altering or initiating the process. 



It is no place here, however, to enter into the many interest- 

 ing problems that artificial parthenogenesis raises, but rather 

 to discuss the narrower cytological ones. 



1 Loeb, J., Artificial Parthenogenesis and Fertilisation. Chicago, I9i3- 



