64 BULLETIN OF THE 



ence of the peripheral layer of protoplasm that is divided into polygonal 

 areas prior to the appearance of the blastoderm. 



Barrois (78) added to what was already known an extended descrip- 

 tion, with figures, of his so-called limuloid stage, and gave notes, without 

 figures, on the development of the germinal layers. 



Balfour ('80) was the first to produce figures of actual sections to illus- 

 trate the history of the germinal layers. Unfortunately, he had no 

 material for the preblastodermic period. 



Sabatier ('81) contributes notes on the formation of the blastoderm, 

 and also on the yolk nucleus of spiders' eggs. 



Schimkewitsch ('8-1) offers the latest contribution to the subject in a 

 preliminary notice in the Zoologischer Ameiger for August 18, 1884, 

 which embraces notes on the entire development. 



I. -The Egg. 



The eggs of Agelena 7i(evia are very abundant in the autumn. Those 

 for the present study were obtained near Cambridge, ^Mass., from Sep- 

 tember 15 to October 15. They exist in cocoons of white silk attached 

 to the underside of fence boards or loosened bark, and in other sheltered 

 places. This species, as well as others, continues to deposit eggs in 

 captivity, thus furnishing a ready means of obtaining freshly laid 

 material. 



Treatment. — For observations on fresh material the long-used method 

 of immersing the eggs in oil is indispensable. The oil should be per- 

 fectly clear and scentless. In hardened eggs the external features can be 

 studied to great advantage by mounting in alcohol after they have been 

 shelled and stained ; the structures previously obscured by the chorion 

 thus become properly exposed. Before using this method I was unable 

 to trace the " rudimentary terga." Another valuable method for surface 

 study consists in clearing the already stained egg in clove oil. I have 

 found this especially appHcable in determining, by means of optical 

 sections, the thickness of the blastoderm on entire eggs. 



In the important work of preparing eggs for cutting, experiments were 

 made with several reagents. The most satisfactory method of treatment 

 proved to be the very simple one already long in use. The eggs were 

 heated in water to about 80° C, and cooled slowly, after which they were 

 passed successively from weak to stronger grades of alcohol. 



Good results were also obtained with Perenyi's fluid, which renders the 

 yolk less brittle, but at the same time changes somewhat its characteris- 



