16 Fertilization and Early Development of Pigeon's Egg 



from the egg nucleus has the chromosomes nearly all fused together. The 

 nearer one is a fused mass of chromatin with a ragged outline showing a 

 decided tendency to form a network. In displaying this tendency it 

 resembles its sister nucleus in the egg. It tends to enter a metabolic 

 phase. The first polar body^ on the other hand, retains the kinetic ten- 

 dency like the second maturition spindle, although it fails to divide. 



The polar ring is present at this stage, but has not been found later than 

 this, being apparently obliterated by cytoplasmic movements occurring 

 within the affected area. 



The sperm nuclei which are found in this egg are rather faintly staining 

 bodies and no one of them is especially near to the egg nucleus. 



The next stage obtained shows the pronuclei very near together, one 

 being slightly smaller and deeper in the egg (the male?) There is a 

 hyaline area adjoining, but no distinct astral appearance (Pig. 10). 



In a later stage the pronuclei, about the same size as in the last in- 

 stance, are seen in contact (Pig. 11). A diagram (Diagram 1), shows 

 the other sperm nuclei present and their distribution. Only one, and it 

 a quite large one, is in the affected area, the rest being scattered away from 

 the center in all directions. 



At a later stage the conjugating nuclei are flattened against each other 

 (Fig. 13). The cytoplasmic surroundings of the disc are shown in the 

 drawing. The peculiar orientation of the lighter staining central area 

 in the form of a cone which was seen in- the maturation stages is not any 

 longer manifested in any of the fertilization stages. There is a con- 

 siderably vacuolated area at one side of the pronuclei and on the other 

 side a curious apparently normal appearance like a hyaline channel ex- 

 tending from the vicinity of the nuclei toward the egg surface. Astral 

 appearances if present are hidden by the yolk. The number of sperm 

 nuclei shown in the diagram (Diagram 2), is only twelve, which is 

 probably too small, as the series of sections was imperfect. 



When the segmentation nucleus is formed the accompanying cytoplas- 

 mic changes in the germinal disc are so striking as to indicate plainly the 

 approach of division (Fig. 13) . The affected area is spread out laterally 

 and shows a differentiation into a more hyaloplasmie margin and a gran- 

 ular interior. This fact is, however, still more clearly perceived by refer- 

 ence to a surface section as shown in the subsequent stage (Fig. 14). 

 The segmentation nucleus (Fig. 13) lies near the center of the affected 

 area, rather closely surrounded by yolk granules. It has moved nearer 

 to the egg surface than at the time of copulation. There are no sperm 

 nuclei remaining within the affected area, but a pair are to he seen a 

 little distance outside of its margin. The segmentation nucleus may be 



