26O LIBBIE H. HYMAN. 



The progressive character of the fertilization reaction has been 

 previously described by a number of investigators. It was first 

 noticed about simultaneously by Fol ('77, '79) an d Calberla 

 ('78). They observed that the detachment and elevation of the 

 fertilization membrane are initiated at the point of attachment 

 of the successful sperm and proceed from there in all directions 

 around the egg. Fol : described this process for Asterias glacialis, 

 Toxopneustes livid us, and Sphcerechinus brevispinosus. Calberla's 

 investigations concern the Petromyzon egg. This egg possesses 

 a micropyle; no change occurs until the sperm has passed the 

 length of the micropyle and touched the surface of the egg cyto- 

 plasm inside the membrane. When this happens the egg with- 

 draws a little from the vitelline membrane at the micropyle and 

 flattens slightly; the separation of the membrane from the egg 

 followed by its elevation then proceeds from the micropyle over 

 the egg. Theel ('92) describes the elevation of the membrane in 

 the sea-urchin Echinocyamus in the following words: "At the 

 place where the first sperm has penetrated the mucilaginous in- 

 vestment, a very thin plasmatic membrane rises and separates 

 from the egg, beginning at the place of contact and extending 

 eventually around the yolk." Herbst ('93) agrees with Fol's 

 description of the fertilization reaction in the sea-urchin egg. 

 Ries ('090) also observed the progressive character of membrane 

 elevation in the sea-urchin egg and presents photographs of the 

 process, taken with a motion picture machine. Elder's drawing 

 of the elevation of the fertilization membrane in Strongylocen- 

 trotus purpuratus shows that this process is a progressive change 

 initiated at one place but Elder does not mention this in the text 

 ('12). Okkelberg ('14) has described the elevation of the mem- 

 brane in the egg of the brook lamprey Entosphenus wilderi. In 

 this egg fertilization occurs at the animal pole and the membrane 

 here separates from the egg. A wave of contraction then passes 

 over the egg towards the vegetative pole, separating the mem- 

 brane from the egg. Just ('19) has given a careful description of 

 the fertilization reaction in Echinarachnius parma. The reaction 



1 There seems to be a prevailing impression that Fol worked with compressed 

 eggs. This is not, however, the case as Fol was at particular pains to state that 

 the eggs were not in the least compressed ("sans les comprimer le moins du monde," 

 '79, p. 176). 



