Membrane Formation 365 



Different Types of Membranes 



Loeb^^ has cited several instances of development w^ithout mem- 

 brane formation in sea urchins and R. Lillie.^^ has mentioned such 

 a case in starfish. The best known case is presented by develop- 

 ment after treatment with hypertonic sea-water. I have repeated 

 this experiment of Loeb's (using 100 cc. sea-water + 15 cc. 2| m 

 KCl for I hour 20 minutes) and find that there are membranes 

 formed on these eggs exactly like those formed on Hipponoe eggs 

 treated with CH3COOH already mentioned. They are very 

 close fitting and might easily escape notice. Membranes which 

 push out only very slightly from the egg surface may be produced 

 by sperm fertilization at high and at low temperatures (15° to 

 20° C. with Toxopneustes at Tortugas, and 32° C. with Arbacia 

 at Woods Hole). The eggs are mixed with the sperm for about 

 one-half minute and then placed in the sea-water at the proper 

 temperature. Cases of development without membrane forma- 

 tion seem to be rather cases of development without pushing out 

 of the membrane. 



Another type of membrane is obtained by allowing eggs to 

 stand at room temperature tor 28 hours. When sperm is added 

 practically all the eggs become surrounded by a thick membrane 

 adhering to the egg surface closely. When the egg divides this 

 surrounds each of the blastomeres, which become quite spherical. 

 Similar membranes are formed by sperm fertilized eggs in Ca- 

 free sea-water. 



That the fertilization membrane is ,.ot present as a surface 

 film in unfertilized eggs which is later pushed out is shown by 

 the fact that unfertilized eggs dissolve completely in concen- 

 trated H2SO4 while fertilized eggs dissolve all but the membranes. 



" Loeb. J. (1) On fertilizing with sperm after 48 hours standing in sterilized sea-water. Pflijgers 

 Archiv. 93, p. 59, 1903. (2) By hypertonic sea-water. Univ. Calif. Pub. Phys., ii. p. 83, 1905. (3) 

 After treatment with pig serum some eggs form no membranes. These mav segment and develop 

 into larvae. Arch. f. d. ges. Physiol. 124, p. 250, 1908. (4) Some eggs of Asterina form no mem- 

 branes after acid treatment, yet develop into small blastulae, Univ. Calif. Pub. Phys. ii. p. 153, 1905. 



^ R. Lillie. .\fter 20 hours in tt^o KCN eggs are warmed. No membranes form yet segmentation 

 takes place. Journ. Exp. Zool. v, p. 386, 1908. 



