422 Avery E. Lambert. 



III. OltlGIN OF TILK GkKISI liAYERS AND FORMATION OF THE 



Cephalic Plate. 



The eggs of Epeira cinerea are slightly elliptical and of a golden 

 yellow color. They are a little less than a inillimeter in diameter. 

 The greater part of the egg consists of masses of yolk, separated from 

 one another by thin sheets of protoplasm which radiate from the 

 center of the egg. These protoplasmic sheets unite above the surface 

 of the yolk where they form a thin layer called the periplasm. 



The entire egg is surrounded by two membranes, an inner, vitel- 

 line membrane, which lies close to the periplasm, and an outer mem- 

 brane, the chorion. The vitelline membrane is thin, delicate, and 

 transparent. The chorion has a tougher texture, the egg bt^iiig seen 

 through it with difficulty. ]joth membranes are supposed to be 

 secreted by the oviducts (Korschelt and Heider, 21). 



Numerous minute globules adhere to the outside of the chorion, 

 giving to it a distinctly granular appearance. That these granules 

 are not structurally a part of the membrane is seen by the fact that 

 when the living egg is immersed in alcohol they float away from it 

 freely. 



Viewed from the surface the yolk masses appear as a group of 

 more or less irregular polygons (Ludwig, 24; Locy, 23; Kishinouye, 

 19). At first there is a slight furrowing of the periplasm, the lines 

 of the furrows coinciding with the edges of the polygonal yolk masses. 

 Later, however, the yolk shifts so that the edges of the masses and 

 the furrows no longer coincide (Kishinouye, 19). 



1. The Formation of the Blastoderm. — It is not possible for me 

 to make a satisfactory statement concerning the earlier stages in the 

 development of the eggs of Epeira, as I was unable to secure enough 

 material of this period for a thorough study ; and I am in doubt if 

 the eggs I did obtain for the earlier stages were normal. Eggs 

 which were killed immediately after being deposited in the cocoon, 

 and sectioned, failed to reveal any traces of a nucleus, a condition 

 also noted by Kishinouye in the material which he studied. 



Shortly after this, however, according to Morin, Locy, and Kish- 

 inouye, a nucleus, surrounded by a mass of protoplasm, appears in 

 the center of the egg. Kishinouye also reports the presence of a 



