THE ECTOPLASM 



on fertilization, bubbles in the cytoplasm break through the 

 surface which undergoes amoeboid changes, then the eggs 

 attain a regular contour.^ Cerebratuhis, a long ribbon-like 

 worm found in the sea, lays eggs in which the cytoplasmic 

 granules in the endoplasm differ from those at the periph- 

 ery.- This egg also displays remarkable amoeboid changes^ 

 which always speak for the 

 presence of an ectoplasmic 

 structure. 



Eggs of the wheel animal- 

 cules or Rotifera according 

 to several investigators show 

 a distinct ectoplasm.^ 



In Yatsu's interesting ac- 

 count of the development of 

 the egg of the mollusk-like 



animal, Lingula,'' is a de- Fig. 8. — Egg of Lingula anatina (after 



tailed description together latsu). 



with pictures showing the surface-located cytoplasm set off 

 from the endoplasm. (Fig. 8.) According to Prouho,*^ the 

 egg of Membranipora possesses delicate projections which 

 he figures. 



In the unfertilized eggs of the echinoderms (starfishes, 

 serpent starfishes, sea-urchins, sea-cucumbers, sea-lilies) 

 the ectoplasm is well defined. Selenka" has described the 

 changes which a sea-urchin egg undergoes before it 

 reaches the stage when it is ready for fertilization. These 



^ Biitschli^ iSjj; also v. Erlanger, iSgiJ and later authors. 



~ Coe, i8gg. 



•^ Andrews., E. A.., iSgj; Wilson^ C. B., iSgg and others. 



■* Zelinka, l8g2; Storch, /g2^ and others. 



'" Yatsu, igo2. 



^ Prouho., i8g2. 



" Selenka, 187S. 



93 



