ON THE DEVELOPMENT OF ARÄ.NEINA. ,57 



The conipositicjji of a freshly hiid egg has been tolerably ac- 

 curately described l)y previous writers, their opinions differing oidy 

 in some points of details. Tt may be conceived of as a scanty network 

 of protoplasm in the wide meshes of which yolk granules are im- 

 bedded. There is always more or less concentration of protoplasm 

 toward the centre which may be called the centroplasm. An ex- 

 tremely thin layer of protoplasm is fnind on the external surface of 

 the egg, directly inside the vitelline membrane and may be dis- 

 tmguished as the periplasm. The centroplasm and periplasm are no 

 doubt connected with each other by a scanty protoplasmic network, 

 although not always ajoparent in sections. The space between the 

 centroplasm and periplasm is almost entirely taken up by large yolk 

 granules which are arranged in characteristic radiate columns. In 

 each column the yolk granules are in several rows, one placed outside 

 another, and in each row there are generally two granules abreast. 

 The granules near the centroplasm are much smaller than those 

 placed more to the outside. In a freshly Jidd egg I was unable to 

 detect the germinal vesicle in any part. The first segmentation 

 nucleus appears in the centroplasm a few hours later. In Lycosa, the 

 so-called yolk-nucleus of tha usual appearance was distinctly seen in 

 the centroplasm. In Agalena, I could not find it. 



The periplasm when seen from the surflxce presents the appear- 

 ance of being divided into irregular polygonal areas (PI. XI, tig. 

 1). The cause of this appearance has lieen a point of dispute, 

 Ludwig* even maintaining that there is no such. That the peri- 

 plasm is marked out into irregular polygonal arears, there can be jio 

 doubt. I agree with Locy** in assigning the cause of this marking 

 to a pressure whicli is exerted on the periplasm and presses it against 



* Ludwig— IJ.'ber die Bildung d"s Blastodermes bei den Spinnen, Zeit, für wiss Zool 

 XXVL 



** Looy— Observations on the Development of Agelena naevia, Bull. Mus. Couip. Zool. XII- 



