10 Fertilization and Early Development of Pigeon's Egg 



into the area formerly occupied by the germinal vesicle. The retreat 

 of the nuclear -wall is unlike ordinary plasmolysis from fixing agents. 

 There is no vacant space left from the shrinking of contents. Such 

 plasmolysis is evident in the case of the younger egg of the pair, Eig. 3, 

 indicating a more watery condition of the nucleus in the younger and 

 still rapidly growing egg. In this egg there are no remnants of threads, 

 except for slight indications upon the more or less rounded nucleoli. 

 The refractive bodies previously mentioned are present. The chromo- 

 somes are shortened as compared with the former instance and are irregu- 

 larly placed. The deutoplasmic microsomes in the nuclear ground sub- 

 stance are less prominent owing to a greater extraction of the stain. 



Underneath the germinal vesicle is a core of lighter staining material, 

 extending inward to the bed of white yolk. The whole germinal area 

 under a low power appears very finely granular compared with the coarse 

 underlying yolk. 



The next stage obtained is that of an egg which in the ordinary course 

 of events would have become free from its capsule and passed into the 

 oviduct in the course of several hours. To be more definite in this 

 instance, the egg was taken from the ovary at 7 :00 P. M., the first egg 

 having been laid in the afternoon. 



The cross section (Eig. 5) shows the equatorial band of chromosomes 

 lying obliquely to the surface of the egg at the margin of the deutoplasmic 

 area. There is an accumulation of a liquid substance at this point 

 between the follicular wall and the granules, which, as in other eggs, may 

 be called the perivitelline liquid. 



The area occupied by the germinal vesicle is obliterated. There is 

 very little if any difference in the appearance of the germinal area at this 

 point, except for the perivitelline liquid above mentioned, and a much 

 greater accumulation of a substance having seemingly the same character 

 directly underneath the finely granular layer. This body of more liquid 

 protoplasm appears in structure and staining properties like the con- 

 tents of the former germinal vesicle. It fills a wider area, however, 

 and is bounded beneath by the coarsely granular yolk. Two eggs were 

 obtained at this stage, both showing the same appearance. It does not 

 appear like an artefact, and though peculiar to this stage of the egg, 

 it seems to be definitely related with later changes in the fertilized egg. 



Ko stages were obtained between those shown in Eigs. 4b and 5. Eig. 

 5 shows the acme of development of the ovarian egg. If the accumu- 

 lation of granule-free protoplasm underneath the granular layer of the 

 disc is derived from the contents of the germinal vesicle, as its appear- 

 ance would indicate, it seems as if a centripetal movement of this sub- 



