Membrane Formation 363 



egg is due to "eine gallertartige Substanz,welche durch vonaussen 

 aufgenonimenes Wasser aufquillt." Loeb" has recently expressed 

 the opinion that an " Eiweisskorper" or hpoid is the substance 

 concerned in the absorption of sea-water and resultant separation 

 of the membrane. 



I had come to similar conclusion this summer before hav- 

 ing read Loeb's or Herbst's papers. The facts are as follows: 

 The fluid between the egg and fertilization membrane has too great 

 a volume to have come from the egg without a corresponding di- 

 minution in size. It must be chiefiy sea-water. It at least contains 

 considerable chlorides (as shown by precipitation with AgNO^). 

 The fertilization membrane is very freely permeable to the salts 

 of sea-water, relativeh' impermeable to sugar and proteids. A 

 small concentration of a sugar or proteid (even though its osmotic 

 pressure were far less than that of sea-water) would be capable of 

 absorbing sea-water through a membrane perfectly permeably 

 to sea-water. 



Donhle Membranes 



I have alreadv mentioned the result we should expect in a 

 h\pothetical sugar cell if the permeability of its membrane should 

 be a second time momentarily increased, namely, a second escape 

 of the reaction product. In the egg a second membrane should 

 be formed by substances causing a second increase of permeability. 

 This actually occurs. Tennenf* has recorded a second mem- 

 brane formed by sperm on starfish eggs which had previously 

 been treated with CO., and formed membranes. I was unable to 

 get the above result in sea-urchin (Toxopneustes) eggs treated 

 with CH^^COOH followed by the addition of sperm. Only those 

 eggs which had been subjected to the acid treatment too short a 

 t me to form membranes could be fertilized. They segmented 

 normally. The spermatozoa were apparently unable to pass 

 ni'imbranes formed by acid. 



'' Loeh, J.: Arch. Eiitwm., xxvi, 1908, p. 82. 

 ^Tfiini-nt; Journ. Exp. Zool., ■^i, 1906, p. 53S. 



