42 



Scientific Proceedings (102). 



of Barber's apparatus and its application to microdissection have 

 already been published. 1 



The egg cells studied consist of a decidedly fluid interior sur- 

 rounded by a more solid surface layer of appreciable thickness. 

 This surface layer is most solid on its external surface. Internally 

 its consistency seems to merge insensibly into that of the fluid 

 interior. The inner surface of this layer adheres to the touch. 

 This is demonstrated by introducing a microdissection needle into 

 an egg and pushing the needle through until its tip comes into 

 contact with the inner boundary of the surface layer on the side 

 of the egg opposite the puncture. On withdrawing the needle the 

 layer adheres to the needle tip and strands are drawn into the 

 interior of the egg. 



If the surface layer be torn while the egg is kept under compres- 

 sion the fluid interior will bulge out through the tear. The 

 cytoplasm, on coming into contact with the surrounding water, 

 tends to establish a definite surface film which prevents the cyto- 

 plasm from mixing with the water. If the internal pressure be not 

 too great this film persists and, in time, strengthens into a definite 

 ectoplasmic layer. The bulge then slowly retracts until the orig- 

 inal contour of the egg is reestablished. If the neck of the pro- 

 truding mass of cytoplasm be small it may pinch off a spherule of 

 cytoplasm which to all appearances is normal. If the internal 

 pressure be too great a succession of films may form as, one after 

 the other, they succumb while the escaping cytoplasm disperses 

 and disintegrates in the surrounding water and the film which 

 finally holds out may enclose only a fraction of the original cell 

 but what it encloses will be normal protoplasm. 2 



Churning of the contents of a mature unfertilized sea-urchin 

 egg causes the ectoplasmic layer to revert to the fluid condition of 

 the interior. The surface film of such an egg is very thin and very 

 easily tears upon which the entire egg disintegrates. On standing, 

 however, the surface film steadily strengthens until the normal 

 condition is reestablished. 



That the distribution of substances throughout the egg cell is 



1 Barber, Philippine Journal of Sc., Vol. X, Sec. B, Tropical Medicine, 1914; 

 Chambers. Biol. Bull., Vol. 34, 1918. 



2 Chambers, Amer. Journ. Physiol., Vol. 43. I9I7- 



