262 LIBBIE H. HYMAN. 



drawing ('12, Fig. 6) of fertilization in S. purpuratus is similar. 

 Gray ('16) speaks of the compression of the egg at fertilization by 

 the contents of the perivitelline space. 



Watching the fertilization process one certainly gains the im- 

 pression that the flattening of the egg is due to a pressure exerted 

 on the egg by the contents of the perivitelline space. It appears 

 that the filling of this space does not occur pari passu with the 

 elevation of the membrane but is due to some other process. 

 This suggests that the accumulation of materials in the perivitel- 

 line space is the direct cause of the elevation of the membrane 

 and such an idea has been advanced by many investigators. 1 

 Further evidence on this matter is desirable. 



4. The Identity of the Vitelline Membrane with the Fertilization 

 Membrane.- This matter has been the subject of some dispute in 

 the history of the fertilization problem. Harvey ('10, '14), 

 McClendon ('11), Elder ('12), Loeb ('13), and recently Gray 

 ('22) have expressed the view that the fertilization membrane is 

 formed by the precipitation or coagulation of materials emanating 

 from the egg on contact with the jelly or the sea-water. That the 

 jelly is not concerned in the appearance of the fertilization mem- 

 brane has been shown by Harvey ('14) and Lillie ('14, p. 553). 



On the other hand the identity of the fertilization membrane 

 with the preexisting vitelline membrane of the unfertilized egg 

 has been maintained by many investigators: Fol ('77, '79) for 

 Asterias, Sphcerechinus, and Toxopneustes, Hertwig ('78) for 

 Asterias, Calberla ('78) for Petromyzon, Theel ('92) for Echino- 

 cyamus, Reighard ('93) for teleost eggs, Herbst ('93, '04) for 

 Sphcerechinus, Echinus, and Stronglyocentrotus, Delage ('01) for 

 Asterias, Schucking ('03) for Asterias and Strongylocentrotus, 

 Ries ('oga) for Strongylocentrotus, Allyn ('12) for Chcetopterus, 

 Glaser ('13) for Arbacia and Asterias, Heilbrunn ('13, '15, '206) 

 for Arbacia and Cumingia, Okkelberg ('14) for Entosphenus, and 

 Chambers ('2ia, '216) for Arbacia, Asterias, and Echinarachnius. 

 Most of these authors rest their view on direct observation of 



1 E.g., Herbst '93, '04, Schiicking '03, Ries '08, 'opa, Loeb '08. It seems clear 

 that the contents of the perivitelline space consist chiefly of water which enters 

 from the outside through the vitelline membrane. This was proved for the lamprey 

 egg by Calberla ('78) by coloring the water and is certain for teleost eggs (Reighard 

 '93). The perivitelline space also appears to contain some colloidal material prob- 

 ably of protein nature derived from the egg. 



