GENERAL PROPERTIES OF THE ECTOPLASM 



spreads from here so that at twenty seconds after insemina- 

 tion — the mixing of eggs and spermatozoa — the whole 

 ectoplasm is cloudy. Now like a flash, beginning at the 

 point of sperm-attachment, a wave sweeps over the surface 

 of the egg, clearing up the ectoplasm as it passes; careful 

 observation reveals that the ectoplasm now shows a brush- 

 work of threads beneath the membrane. Twenty-five 

 seconds after insemination, a cone of ectoplasm protrudes 

 from the egg and encloses the sperm-head. This is sud- 

 denly pulled into the cone; the ectoplasmic threads break at 

 the site of sperm-attachment and release the membrane. 

 Progressi^'ely from this point the membrane separates in a 

 wave from the surface of the egg, leaving in its wake collaps- 

 ing ectoplasmic strands. Thirty seconds after insemination 

 the membrane is separated from the egg by a narrow peri- 

 vitelline space. During the ensuing twenty-five seconds 

 this space increases in width; the ectoplasmic strands 

 become more sharply defined giving the ectoplasm the 

 appearance of a striated layer. The vitelline membrane 

 becomes equidistant from the Q.gg at all points and the 

 perivitelline space is at its greatest width one hundred 

 twenty seconds after insemination. 



This progressive lifting of the membrane, first noted by 

 Derbes,' I have studied in several species of eggs in great 

 detail.- On the basis of experiments with physico-chemical 

 means which induce membrane-separation, certain investi- 

 gators ha\'e simply assumed the de novo origin of the mem- 

 brane which thev called the "fertilization-membrane." 

 However, careful observation shows, as described above, that 

 the membrane is already present on the egg and separates 

 at fertilization by a progressive wave beginning at the point 

 of sperm-entry. It thus is not a "fertilization-membrane," 



^ Derbes, 1847 . See also Fol, iSyg. 



-Just, JQiQa, ig2i, i()22e, ig2Sc and f, ig2ga and b. 



105 



