STUDIES IN ARTIFICIAL PARTHENOGENESIS. 345 



Thus, although this phrase is in general use, I have discarded it 

 in preference for the more truly descriptive term "elevation." 

 This is in accord with the German practice. 



Loeb claims that the process of normal membrane elevation 

 is too rapid for observation. It is necessary to retard the process 

 by cooling to 3 or 4, when, on fertilization under these condi- 

 tions, small rounded elevations, the so-called "bubbles" appear 

 on the egg surface; these flow together and their fused outer 

 boundary becomes the vitelline membrane. A similar effect is 

 observed on treatment with butyric acid. I believe that bubble 

 formation is abnormal, and I shall consider its true cause later. 



In the fertilized egg the space between the vitelline membrane 

 and the egg is known as the perivitelline space (Membranraum). 

 Some few minutes after fertilization a hyaline layer appears to 

 be differentiated at the external border of the cytoplasm. This 

 is the hyaline layer (ectoplasmic layer, etc.). 



The importance of a study of membrane elevation is twofold. 

 In the first place, it may serve as a device for the prevention of 

 polyspermy in normal fertilization, and is, therefore, of physio- 

 logic significance. Secondly, in recent years, this process has 

 played an important part in theories of fertilization and artificial 

 parthenogenesis. Robertson 1 goes so far as to confuse membrane 

 elevation with fertilization, considering the two as synonymous. 



Although from time to time various ingenious hypotheses 

 have been advanced to explain membrane elevation, the only 

 theory at all plausible was advanced by Fol 2 who was the first 

 ever to consider the problem. Before discussing Fol's view I 

 shall first mention several other explanations which have been 

 suggested. Schiicking 3 thought that the preformed membrane 

 was split by the absorption of water, so that a double membrane 

 was produced on fertilization. Such a process would be difficult 

 to explain physically, and no one has ever attempted to do so. 

 Fischer and Ostwald 1 regard membrane elevation as due to the 

 exit from the egg of a fluid which is given off as a result of 

 coagulation of a portion of the protoplasm. The rapidity with 



1 T. B. Robertson, Arch. f. Entw. Mech., XXXV., 64 (1912). 



2 Fol, Mem. d. 1. Soc. d. phys. et d'hist. not. d. Geneve, XXVI. (1879). 



3 Loc. cit. 



4 M. Fischer ^nd Wo. Ostwald, Arch. f. d. ges. Physiol., CVL, 229 (1905). 



