THE ECTOPLASM 



It thus seems practical to speak instead of kinds of 

 plasma, of zones of the cell-body and we can distinguish: 

 A central condensed zone. ... A zone of network. . . . A 

 hyaline cortical zone. . . . ^ 



In the egg of teleosts (bony fishes) the protoplasm, at 

 first a thin sheath enclosing the yolk, moves at fertilization 

 to one pole to form a disc leaving only a delicate layer to 

 surround the remainder of the yolk mass.- Here the rela- 

 tions are as in the eggs of cephalopods. 



Living eggs of amphibians (frogs, toads, salamanders) 

 have been long recognized as showing a differentiated 

 surface due to the presence of pigment extending over 

 approximately one-half the egg. In sections amphi- 

 bian eggs show further differentiation of the superficial 

 cytoplasm.'^ 



In the eggs of both reptiles and birds the protoplasm is 

 sharply set off from the large mass of inert yolk. The 

 description given by His for the selachian egg and quoted 

 above applies to the eggs of reptiles and birds. 



Recently, Lewis and Hartmann have described the 

 organization of the living egg of the monkey."* Other eggs 

 of mammals, as that of the mouse, bat, rabbit, etc., also 

 show some difference between the peripheral and the 

 central cytoplasm. 



In addition to these accounts which describe eggs of 

 every group of animals as having ectoplasm, we should note 

 those studies which show that ectoplasmic structure is 

 revealed by experimental treatment. Hammar's descrip- 

 tion of the ectoplasm on the sea-urchin's tgg as composed of 

 radial striations was based on observations on eggs in 



1 His, 1897. 



" List, iSSj. This process was very beautifully described as 

 early as 18^4 by the English physician, Ransom. 

 ^ King, igoi. Earlier: Goette, 187^. 

 •* Lewis and Hartmann, IQJJ. 



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