The biology of the cell surface / by Ernest Everett Just.

  • Ernest Everett Just
Date:
[1939]
Catalogue details

Licence: Public Domain Mark

Credit: The biology of the cell surface / by Ernest Everett Just. Source: Wellcome Collection.

    110/416 page 92
    can easily confirm under low power of an ordinary microscope. Indeed, I have with the naked eye seen the green cytoplasm on this rather large egg; also have I found that under pressure the endoplasm, which Kowalew- sky did not consider living substance, will stream out as the large egg ruptures leaving the green surface-cytoplasm intact. The difference between the peripheral and the inner cyto- plasm of eggs of flat-worms has been often observed,1 though some authors fail to do so, and still others have expressed the opinion that the structural differentiation observed might be due to fixation.2 Many flat-worm eggs present serious difficulties for study in the living state because they are laid in capsules each containing several eggs; removal of the eggs from the capsule may mean their injury. In addition, because of opacity, they do not always lend themselves to observation of their finer structure. Nevertheless, one may assert that eggs of turbellarians and trematodes and even of those of cestodes (tape-worms) exhibit a resolution of the cytoplasm into an endoplasmic and an ectoplasmic region, as Metschnikoff, Selenka, Lang, Pereyaslowzewa and Janicki, among others, have shown. The thread-worms, nematodes, include Ascaris, a para- sitic worm which has been the object of many researches and which will come up for reference frequently in this book. The unfertilized egg of Ascaris shows, accord- ing to Van Beneden and Meves, ectoplasmic differen- tiation; irregular in shape, after fertilization it becomes spherical having in the meantime secreted a substance which forms an enclosing shell. The eggs of free-living nematodes, closely allied to Ascaris, show a similar change; 1 Metschnikoff, i88j; Selenka, i88j; Lang, 1884; Pereyaslowzewa, 1892; Warren, 190J; Janicki, /pop. 2 Hal kin, 1902.
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