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 lif ting-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. 1 



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." 2 On this assump- 

 tion the colloidal substance which undergoes the swelling would 

 be the substance whose removal gives rise to the development. 



F. Lillie 3 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 colloid 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 megalocephala 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 Bio- 

 chemie, II, 100, 1909. 



s Lillie, Jour. Morphol., XXII, 361, 1911. 



