12 ATLAS OF THE FERTILIZATION AND KARYOKINESIS OF THE OVUM. 



Plate I. Phototype 3. 



TJic first Polar Karyokinetic Figure. 



This figure shows the egg (taken from the ovary) during the formation of the first polar body. An amphiaster 

 lias been formed with its axis directed radially toward the surface. The germinal vesicle and germinal spot have 

 disappeared and a large portion of the chromatic substance, including the germinal spot, has been converted into 

 cytoplasm. The remaining portion, which constitutes but a fraction of the original chromatic network, is aggregated 

 to form a group of chromosomes surrounding the equator of the spindle. These chromosomes are arranged in 

 groups of four, — the so-called " Vierergruppcn'' or tetrads, which are characteristic of the formation of the first 

 polar body. (See p. 9.) Their number, which is probably 18 or 19, cannot be made out in the figure. The 

 polar body will be formed at the surface of the ovum (see Fig. VII.), receiving the upper aster with the corresponding 

 spindle-half and half of each tetrad. The second polar body will subsequently be formed at the same point. 



Plate I. Phototype 4. 

 The Mature Egg after the Formation of the Polar Bodies. 



The chromosomes remaining in the egg after the formation of the second polar body have become transformed 

 into the egg-nucleus, which appears as a clear vesicle lying in the upper portion of the egg. (The polar bodies, 

 which normally lie at the nearest point of the periphery, have become detached from the egg and are not visible.) 

 The egg-protoplasm (cytoplasm) contains at this period a number of rounded dark bodies stained intensely blue 

 by haematoxylin, the meaning of which is not clear. They may perhaps represent the degenerating chromatin not 

 used in the formation of the polar bodies and set free from the germinal vesicle at the time the first polar body is 

 formed. They may perhaps represent yolk-substance (deutoplasm) and form a reserve supply of food. Neither of 

 these views is satisfactory, however, and the real significance of these yolk-bodies remains in doubt. 



The egg-nucleus, which is very sharply defined, contains a delicate reticulum of Hnin (not visible in the figure, 

 since it is not stained by the haematoxylin) in the meshes of which are suspended numerous distinct rounded 

 chromatin-granules. The membrane at this period consists of two elements, an outer achromatic layer not visible 

 in the photograph, and an inner chromatic layer composed of chromatin-granules. The inner layer probably is to 

 be regarded as merely the peripheral portion of the general network. 



