58 K. KISHINOUYË. 



the peripheral end of the underlying yolk columns, thus causing the 

 former to receive the impression of the latter. The fact that in 

 freshly laid eggs the polygonal areas correspond with the underly- 

 ing groups of yolk granules favours tliis view. I must, however, 

 differ from Locy as to the cause of this pressure brought to bear on 

 the periplasm. Locy ascribes it to the contraction of the egg. This 

 can hardly be, for I could find in no case any trace of contraction, the 

 eggs being always very closely covered by the two membranes. I 

 think it much more probable that the polygonal markings are the 

 effect of the pressure to which the eggs are subjected as they pass 

 through the narrow oviduct. Locy states moreover that at an early 

 stage a number of faintly marked areas made their appearance at the 

 animal pole, ^vhile they could not be detected upon the opposite 

 hemisphere. I can not corroborate this statement, for I found the 

 polygonal marking covering the whole surface of the eggs from the 

 earliest period after l^eing laid. It should be stated that after a while 

 when segmentation begins, the yolk granules more or less shift tlieir 

 places ; hence we no longer find the coincidence of polygonal areas 

 with groups of yolk granules. The polygonal areas do not seem to 

 change their positions nor do they vary in number after they are 

 once formed. 



From the Segmentation of the Ovum to the Formation 

 of the Germinal Layers. 



According to Ludwig*, who gives a detailed description of the 

 segmentation of the ovum in Philodromus, the nucleus and the yolk 

 divide simultaneously first into two, then into four, eight, sixteen, 

 nnß. so on. Morin** who studied Theridion, IMiolcus. Drassus and 



* Ludwig — loc. cit. 

 ** Moïin — Zur Eutwicklungsgeschichte dey Spinnen, Biolog-. Centralbl. VI. 



