is found the most important part of the egg, the cocks' 

 trace or cover (cicatricula) . It consists of a thin surface 

 disk, which Pander had called "the rudiment pellicle" 

 (Keimhaut, blastoderma) , but which Baer preferred to label 

 the rudiment (Keim, bLastos) . The rudiment is composed of 

 firmly laid small whitish granules, under which lies the 

 rudiment layer, whose whitish-yellow mass Pander called 

 the nucleus of the cover. Baer considered all this to be 

 only layers of the yolk, which connect with the rudiment and 

 merge with the remaining yolk. Only in the middle is the 

 nucleus of the cover separated from the yolk by fluid to 

 form the hillock of the rudiment layer. 



The formation of the yolk ball (§ 3) Baer traced from 

 its presence in the nonsexual ly mature hen; such a hen's 

 ovary contains vesicles with transparent fluid. Reaching 

 the size of a millet grain or seed, the vesicles sharply 

 increase in size and become filled with a milky white, then 

 yellowish content at copulation. The yolk is connected to 

 the ovarian stem and is covered with a capsule composed of 

 firmly adjoined layers. These layers have openings for 

 vessels which do not, however, penetrate the yolk; thus 

 the yolk membrane remains intact. At the emerging part of 

 the yolk, which is still in the ovary, an arch-shaped white 

 zone-— cicatrice — appears. When the yolk is ready for 

 separation, the ovarian membrane ruptures in the region 

 of the cicatrice. After the yolk exits from the capsule, 

 its remains and stem form a deepening, called the cup. The 

 membrane directly covering the yolk appears on its surface 

 before maturation. Also long before maturation, near a 

 small yolk equator (beside the cup stem, sometimes at the 

 cicatrice), a white spot appears, corresponding to the cover 

 of the laid egg. But in the ovarian egg it does not acquire 

 such clear outlines. This part is called the rudiment layer. 

 In its middle there is a light spot, an extremely delicate 

 vesicle filled with a transparent fluid, called the embryonic 

 vesicle or Purkinje vesicle. 



The term "embryonic vesicle" (for the egg nucleus) was 

 widely employed in embryological literature until recently, 

 and even in current works. Baer noticed that in hens the 

 embryonic vesicle is revealed very early, while the corre- 

 sponding transference of the nucleus takes place at a much 



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