216 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
e.g., Asterina. It may seem pedantic to discriminate between the 
membrane formation and the process underlying it: but this discrimi- 
nation is suggested by a suspicion on my part that the membrane 
formation is the result of a process of secretion of a liquid from the 
egg; and that this secretion or the throwing-out of certain substances 
of the egg is the important feature, while the lifting-up of the surface 
layer of the egg (the membrane formation proper) is only a mechanical 
consequence of this secretion, but of no importance in itself.! 
The same idea was repeated by the writer a little later in 
the following words: ‘‘We might think of the possibility that _ 
an elimination of a definite inhibiting substance sets into motion 
the chemism, which underlies development.” On this assump- 
tion the colloidal substance which undergoes the swelling would 
be the substance whose removal gives rise to the development. 
F. Lillie? has recently found that a layer of substance, 
which in the unfertilized egg of Nereis lies under the natural 
vitelline membrane of the egg, flows out (is ‘‘secreted’’) and 
forms a thick gelatinous layer around the egg, as soon as the 
spermatozoon comes in contact with the egg. But this gelati- 
nous layer resembles the gelatinous envelope which surrounds 
the frog egg and does not form a tough membrane at its outer 
surface, such as we observe in the sea-urchin egg. 
Lillie assumes 
that the presence of this eclloid substance in the cortex is an inhibition 
to the maturation of the egg, because as soon as it is removed, matura- 
tion processes are set in motion and both polar bodies formed. In 
what manner it inhibits is of course problematical. In the egg of 
Ascaris megalocephaia there is a similar excretion of a cortical colloid 
which forms, in this case, the thick resistant perivitelline membrane. 
The appearance of the fertilization membrane of echinids might be 
similarly due to excretion of a cortical colloid which is removed by 
diffusion and hence is not detected. 
1 Loeb, ‘Artificial Membrane Formation and Chemical Fertilization in a 
Starfish.’ University of California Publications, Physiology, II, 154, 1905; reprinted 
in Untersuchungen zur kiinstlichen Parthenogenese, p. 362, Leipzig, 1906. 
2 Loeb, ‘‘ Die kiinstliche Parthenogenese,’’ Oppenheimer’s Handbuch der Bic- 
chemie, II, 100, 1909. 
‘ Lillie, Jour. Morphol., X XII, 361, 1911. 
