STUDIES IN ARTIFICIAL PARTHENOGENESIS. 163 



brane elevation. At a later point, in discussing what I believe 

 to be the true explanation of membrane elevation, I shall en- 

 deavor to point out a reason for this sequence. 



C. Theories of Membrane Elevation. 



The problem of membrane elevation is quite distinct from 

 that of segmentation, which is the central theme of the study 

 of artificial parthenogenesis. No method of producing mem- 

 brane elevation ordinarily results in more than one or two per 

 cent, of segmentations, and many methods usually result in 

 no segmentations whatsoever (e. g., chloroform, urethane). 

 Moreover, some of the best methods for producing segmentation 

 do not involve membrane elevation: thus hypertonic sea-water 

 never results in an elevation of the membrane. 



Of late Loeb has been of the opinion that membrane "forma- 

 tion," involves the swelling of some substance at or near the egg 

 surface. To quote from his book 1 "a colloidal substance which 

 lies below the surface layer of the unfertilized egg or is secreted 

 from the egg, suddenly swells by absorption of sea-water. In 

 the typical case of membrane formation this swelling results finally 

 in a complete liquefaction of the colloid. In other cases the 

 swelling is less complete and the formation of a gelatinous film 

 results." Loeb thus regards the process of membrane formation 

 as due to the swelling of a colloid, concerning the position of 

 which he is not quite clear. On page 213 of the same book he 

 says it is in the cortical layer. Finally, if the egg is left too long 

 a time in a solution which causes membrane formaton, not only 

 a colloid at the periphery, but colloids throughout the egg swell, 

 and cytolysis results. 



In the discussion of Loeb's theory, I shall assume that he 

 uses the word "swell" in its colloid-chemical sense, i. e., to de- 

 note the absorption of a liquid (in this case water) by a gel. 

 Of course any less specific use of the term would rob the theory 

 of all theoretical significance. Briefly, the objections to the 

 swelling theory, as upheld by Loeb, are: 



I. All the reagents which cause membrane elevation can 

 scarcely induce the swelling of any one colloid. Loeb claims 



1 Loc. cit., p. 210. 



