STUDIES IN ARTIFICIAL PARTHENOGENESIS. 159 



the egg surface. This is the well-known process of membrane 

 elevation, or, as it is usually spoken of in this country, membrane 

 formation. During elevation, the membrane under normal 

 conditions does not undergo any evident increase in thickness. 

 The inner border of the vitelline membrane is often not very 

 plainly visible. In order therefore to estimate the thickness of 

 the membrane after elevation, it is convenient to compress the 

 eggs gently. The egg then becomes pushed out against the 

 vitelline membrane, in some directions at least, and the distance 

 between its outer border (i. e., the hyaline layer, see below) 

 and the outer boundary of the vitelline membrane is a measure 

 of the greatest possible thickness of the membrane. Under such 

 conditions, high power examination showed that the thickness 

 of the elevated membrane is approximately the same as that 

 of the unelevated membrane. Quantitative measurements were 

 not found to be practicable. 



Moreover, after elevation the membrane still retains the 

 same chemical properties that distinguished it before fertiliza- 

 tion. In dilute HC1 it swells rapidly, and soon becomes sticky. 

 Nal also induces the elevated membrane to swell, much as it 

 did before fertilization. 



After the vitelline membrane has been lifted from the egg 

 surface, a new membrane appears around the cytoplasm. This 

 structure has received an unusually large number of names; 

 of these I shall use the term "hyaline layer." It seems reason- 

 able to conclude that its formation depends on the same pre- 

 cipitation reaction which produces the membrane about egg 

 fragments, and which is probably also responsible for the vitel- 

 line membrane. This conclusion is supported by the fact that 

 it shows semipermeable properties. 



The process of membrane swelling has often been confused 

 with that of membrane elevation. This is perhaps due to the 

 ambiguity of the term membrane formation. It has been the 

 custom to apply the term whenever the observer notices some- 

 thing at the egg surface which he did not see at the beginning 

 of the experiment. But membrane swelling and membrane 

 elevation are two very different processes and are usually 

 easily distinguishable under the microscope. The elevated 



