266 LIBBIE H. HYMAX. 



elevate fertilization membranes but that these processes are 

 confined to the cortical portion of the ruptured egg. He further 

 states that if the extra-ovate remains in continuity with the 

 cortical portion for some time it becomes fertilizable but still 

 does not elevate a membrane. I have produced extra-ovates in 

 5 1 . franciscanus with the needle; upon fertilization the cortical 

 portion elevates a membrane while the extra-ovate does not 

 (Fig. 18). 



From all of these observations it may be concluded: (a) that 

 the vitelline membrane is identical with and is elevated as the 

 fertilization membrane; (b] that the vitelline membrane is a 

 definite morphological structure which cannot be reformed or 

 replaced; 1 and (f) that the fertilization reaction, which includes 

 other visible changes besides membrane elevation, is exhibited 

 only by the cortex of the egg. 2 



Since the fertilization membrane is thus a preformed, pre- 

 existent structure, its separation from the egg at fertilization 

 should be spoken of as membrane elevation and not as membrane 

 formation. The advisability of this terminology was previously 

 emphasized by Heilbrunn ('15). 



When the vitelline membrane elevates as the fertilization 

 membrane, however, it unquestionably undergoes certain phy- 

 sical and chemical changes. In the first place it would seem that 

 the membrane must soften since in elevating it is distended 

 considerably beyond its former circumference. A number of 

 observers have attested that there is no decrease in size of the 

 echinoderm egg at fertilization (Fol '79, Theel '92, Herbst '93, 

 Schiicking '03, Ries '08, Loeb '08, McClendon '10, Chevroton and 

 Vies 'n, Gray '16, Chambers '216). I was also unable to find 

 any change in size of the eggs of 5. franciscanus on fertilization. 



1 Any portion of the egg cytoplasm does of course when exposed to sea-water 

 form a protective surface layer which has no doubt physiological properties similar 

 to those of the vitelline membrane but which is not elevatable by sperm. Several 

 observers (Herbst, '03, Tennent and Hogue, '06, Harvey, '10, Heilbrunn, '206) 

 have recorded that a second membrane can be elevated after the elevation of the 

 usual fertilization membrane by treatment with various agents (but not with 

 sperm). This second membrane is in reality the hyaline layer, as also stated by 

 Harvey ('14) and Heilbrunn ('206). 



2 The importance of the cortex finds explanation on the basis of Lillie's fertilizin 

 theory (cf. Lillie, '19, also Chambers. '216). Just ('23) also shows that the fertiliza- 

 tion reaction is confined to the cortex. 



