THE BIOLOGY OF THE CELL SURFACE 



plasma-layer which though it has often been described^ 

 (Fig. lo) has never, as we shall see in the chapter on cell- 

 division, been properly interpreted by those who have 

 observed it, and generally been misunderstood by those 

 who have on the basis of experiments on it made theories 

 concerning its role. For eggs of the brittle starfishes and 

 of the sea-cucumbers, Selenka has given good descriptions, 



pointing out that the layer is 

 most pronounced in eggs of the 

 brittle starfishes, less in those 

 of sea-urchins and least in sea- 

 cucumbers'. I find that in 

 these as in the eggs of the 

 starfish the ectoplasm can 



Fig. io. Fig. ii. 



Fig. io. — Egg of Echinocyamus pusillus (after Theel) to show structure of 

 ectoplasm after full separation of vitelline membrane following penetration of 

 a single spermatozoon. 



Fig. II. — The ectoplasm of the egg of Rhynchelmis limosella (after Vejdovsky 

 and Mrazek). 



always be distinguished in sectioned eggs fixed with certain 

 reagents for then minute granules appear; also the delicately 

 radial structure is evident. 



1 turn now to the eggs of the segmented worms. Very 

 strikingly does the ectoplasm differ from the endoplasm in 

 the egg of Rhynchelmis'^ as pictured here (Fig. ii). But no 

 less clearly or remarkably do the inner and outer regions in 

 the egg of Phascolosoma^ reveal themselves. The ecto- 



^ Hertwig, i8j6; Selenka, i8y8; Fol, iS/p; Ludwig, 1880; 

 Selenka, i88j; Berthold, 1886; Theel, i8g2; Hamrnar, 1896; 

 Andrews, /c?p7; Ziegler, 1904; Meves, 1914. 



2 Vejdovsky, 1892; Vejdozvsky and Mrazek, 1903. 

 ^ Gerould, 190"/; Bergmann, 190^, on annelids. 



96 



