THE BIOLOGY OF THE CELL SURFACE 



the outer sheath of cytoplasm contains large granules, 

 whilst in that of Mytilus according to Meves' figures the 

 ectoplasm in the fixed egg is a clear margin bounded by a 

 homogeneous and apparently firmer sheath of cytoplasm 



beneath the very thin vitelline mem- 

 brane. In figures of the eggs of Chiton 

 also one distinguishes ectoplasm from 

 endoplasm. In addition, my observa- 

 tions convince me that in the eggs of the 

 razor clam, Ensis, and of the small clam, 

 Cumingia, the outer region of the cyto- 

 plasm differs from the inner. The large 

 ellipsoid eggs of cephalopods — ink-fishes 

 and allies — show a disc of clear cytoplasm 

 containing the nucleus at the upper more 

 pointed end which is continuous with a 

 very thin layer enclosing the inert yolk. 

 Disc and layer constitute the active sub- 

 stance of the egg; in them development 

 ensues; it is as though the cytoplasm in 

 these eggs were all ectoplasm. 



Among eggs of arthropods are those of 

 insects,^ whose ectoplasm is even more 

 strongly marked than that in eggs of 

 Fig. 14.— Egg of //y- coelenterates. Beyond we shall note 



drophilus pisceus (after , , ^ , , 



j^gjjgx that the ectoplasm 01 these eggs has most 



interesting behavior. Appended is a 

 picture from Heider showing the ecto-endoplasmic differ- 

 entiation in the egg of a beetle (Fig. 14). Eggs of other 

 arthropods clearly show ectoplasm. ^ 



Among the lowest forms of Chordates, the Ascidians, 

 we find that the beautifully transparent egg of Phal- 



1 Heider, i88g. 

 - Groom, 1894. 



98 



