24 THE EMBRYOLOGY OF INSECTS AND ARACHNIDS. 



appears to be a swelling with a depression on its apex. However that may be, the 

 central portion of the spot has a different refractive index from the peripheral portions. 



Figures LXIX and LXIX' represent a later stage in the maturation of the egg 

 drawn with a low and a high power. 



The germinal vesicle at this stage has lost its definite boundary and shades off 

 into the yolk spherules. 



The ovarian epithelium has grown round and nearly closed the outer pole of 

 the egg. 



Through the opening still left by the ovarian epithelium the remaining un- 

 absorved nutritive cells are probably taken in. The germinal spot, at this stage, 

 differs from the same structure in earlier stages. This, however, may be due to the 

 different action of hardening fluids or to differences in preservation, etc. 



Sections of the mature egg showed no traces of the germinal vesicle or spot. 

 The latter, as we may believe from Hertwig's (1 - observations on the maturation of 

 the ovum, might readily persist and yet be overlooked, owing to its small size and 

 to the confusion resulting from the number of yolk spherules. Will <2) in the article 

 referred to describes the migration of the vesicle of this egg to the periphery where 

 it loses it boundary and runs into the yolk. He thinks the germinal spot also 



disappears. 



ARACHNID A. 



The observations made on the embryology of spiders were not complete, but 

 they have brought to light some interesting points not heretofore noticed or suffici- 

 ently emphasized. No observations were made on the early stages of segmentation. 

 The observations of Ludwig on the early stages of development do not, as before 

 stated, fully accord with those of other observers. Schimkewitsch agrees with 

 Balfour in thinking that on the formation of the blastoderm some undifferentiated 

 cells remain in the yolk cells. The observations recorded here do not settle this 

 point however. 



Before the formation of the blastoderm, the so-called primitive cumulus is 

 formed on the surface of the egg. 



At this stage there are cells undergoing division in the yolk (YG Fig. LXXV). 



(i) Hertwig. Morphologishes Jahrbuch Vol. III. 



