256 LIBBIE H. HYMAN. 



in fact, of solid consistency, as fluids do not exhibit permanent 

 wrinkles. These wrinkles on egg fragments are illustrated in 

 Figs. 10 and 13. In only one case did the entire membrane per- 

 sist after disintegration of the cytoplasm; this case is illustrated 

 in Fig. 16. The membrane is collapsed and wrinkled. 



In the Patiria egg, when punctured as just described, the cyto- 

 plasm flows out invariably leaving the membrane behind. This 

 is illustrated in Figs. 19 to 25. From the fact that the membrane 

 always persists in the starfish egg after disruption of the cyto- 

 plasm and rarely so persists in the urchin egg, I have drawn the 

 conclusion that the vitelline membrane of the former egg is 

 firmer, tougher, and probably thicker than in the latter egg. 

 This difference is further evidenced by the fact that the empty 

 membrane in Patiria retains its former shape better than in the 

 urchins as may be seen by comparing Figs. 16 and 19. 



The consistency of unfertilized eggs has been previously de- 

 scribed by a number of investigators. The first detailed descrip- 

 tion of the viscosity conditions in unfertilized eggs seems to have 

 been that of Herbst ('93). Herbst noted that if pressure is 

 applied to unfertilized sea-urchin eggs, the contents flow out 

 and a fine membrane is sometimes left behind to which bits of 

 protoplasm still cling. He therefore concluded that the surface 

 layer of the egg possesses a greater consistency than the remainder 

 of the egg but is not definitely separated from the latter. Lillie 

 ('06) notes that the Chcetopterus egg is semifluid and surrounded 

 by a delicate membrane. Heilbrunn ('15) states that the cyto- 

 plasm of the unfertilized Arbacia egg is "typically fluid" and 

 inclosed in a membrane described as being "a protein gel" and 

 possessing "a certain degree of rigidity." Chambers ('170) finds 

 that the protoplasm of the unfertilized eggs of Arbacia, Asterias, 

 Echinarachniiis, Cerebratulus, and Fucus is a "hyaline fluid" of 

 "very slight consistency" while the surface layer is "very dense 

 in consistency as compared with the cell interior into which it 

 merges insensibly." Chambers has also noted the greater 

 delicacy of the membrane of the urchin egg than of the starfish 

 egg ('2 1 b). Heilbrunn (*2O&) describes the Cumingia egg as "a 

 mass of fluid protoplasm surrounded by a rigid membrane." 

 Seifriz ('18, '20) finds that ripe Fucus eggs are decidedly viscous 

 with a wall consisting of a very rigid hyaline gel; he also describes 



