Artificial Parthenogenesis 251 
as in the domain of fertilisation. The reader knows that the eggs of 
the overwhelming majority of animals cannot develop unless a 
spermatozoon enters them. In this case a living agency is the cause 
of development and the. problem arises whether it is possible to 
accomplish the same result through the application of well-known 
physico-chemical agencies. This is, indeed, true, and during the last 
ten years living larvae have been produced by chemical agencies 
from the unfertilised eggs of sea-urchins, starfish, holothurians and 
a number of annelids and molluscs ; in fact this holds true in regard 
to the eggs of practically all forms of animals with which such 
experiments have been tried long enough. In each form the method 
of procedure is somewhat different and a long series of experiments 
is often required before the successful method is found. 
The facts of Artificial Parthenogenesis, as the chemical fertilisa- 
tion of the egg is called, have, perhaps, some bearing on the problem 
of evolution. If we wish to form a mental image of the process of 
evolution we have to reckon with the possibility that parthenogenetic 
propagation may have preceded sexual reproduction. This suggests 
also the possibility that at that period outside forces may have 
supplied the conditions for the development of the egg which at 
present the spermatozoon has to supply. For this, if for no other 
reason, a brief consideration of the means of artificial partheno- 
genesis may be of interest to the student of evolution. 
It seemed necessary in these experiments to imitate as completely 
as possible by chemical agencies the effects of the spermatozoon upon 
the egg. When a spermatozoon enters the egg of a sea-urchin or 
certain starfish or annelids, the immediate effect is a characteristic 
change of the surface of the egg, namely the formation of the so-called 
membrane of fertilisation. The writer found that we can produce 
this membrane in the unfertilised egg by certain acids, especially the 
monobasic acids of the fatty series, eg. formic, acetic, propionic, 
butyric, etc. Carbon-dioxide is also very efficient in this direction. 
Tt was also found that the higher acids are more efficient than 
the lower ones, and it is possible that the spermatozoon induces 
membrane-formation by carrying into the egg a higher fatty acid, 
namely oleic acid or one of its salts or esters. 
The physico-chemical process which underlies the formation of 
the membrane seems to be the cause of the development of the egg. 
In all cases in which the unfertilised egg has been treated in such a 
way as to cause it to form a membrane it begins to develop. For 
the eggs of certain animals membrane-formation is all that is 
required to induce a complete development of the unfertilised egg, 
eg. in the starfish and certain annelids, For the eggs of other 
animals a second treatment is necessary, presumably to overcome 
