. The biology of the cell surface. Cytology. 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 i
. The biology of the cell surface. Cytology. 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. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Just, Ernest Everett, 1883-1941. Philadelphia, P. Blakiston's son & co. , inc
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