13 Fertilization and Early Development of Pigeon's Egg 



are a resting stage of the chromatin. According to the opinion of Wil- 

 son^ 00, such nucleoli are to be regarded as chromatin masses distinct 

 in nature from true nucleoli or plasmosomes. In the smaller pigeon 

 ova such net-knots of chromatin are frequently seen, looking like the 

 beginning of the formation of a nucleolus or the contrary, the unrolling 

 of one to form a thread (Pigs, la and b). But better evidence on the 

 nature of these chromatin nucleoli may be obtained from other material 

 than the pigeon. Without going too far afield from the purpose of this 

 paper, it may be mentioned that the ova of the sparrow in the winter 

 condition give an excellent example of chromatin aggregated into the 

 form of nucleoli. There is an almost entire disappearance of the chro- 

 matin network and a large and variable number of nucleoli having the 

 staining reaction of chromatin. This phenomenon is accompanied by 

 a watery condition of the nucleus as shown by the great plasmolyzation 

 from fixing agents. The eggs may be fixed so as to show no distortion, 

 but the nuclei are invariably plasmolyzed. 



This condition disappears when the growing season recommences in 

 March. The chromatin threads reappear and the nucleus is no longer 

 so easily plasmolyzed. The difference between the pigeon and the spar- 

 row ova is accounted for by the fact that the ovary of the sparrow is 

 in a resting state in the winter, while the breeding season of the pigeon, 

 in comfortable quarters, is continuous except for a slight cessation in 

 the fall, during moulting. If the view of Carnoy and Le Brun is correct, 

 the evidence for the continuity of the chromosomes through the ovarian 

 development alleged by Born, 94, must be mistaken. 



A frequent appearance found in the pigeon ova was that of pale, 

 broken-down nucleoli, looking rather like the " shells " of nucleoli, either 

 inside the nucleus or outside close to the mSmbrane. This appearance is 

 entirely different from that of the previously described refractive bodies. 

 Such bodies are described by Carnoy and Le Brun in the amphibian egg. 



The Peetilized Egg. 



Maturation Divisions. — The earliest stage of the fertilized egg obtained 

 is shown in horizontal section in Pigs. 6a and b. The surface appear- 

 ance of the disc of such an egg is shown in Pig. 6. The slightly oval 

 disc has a greater diameter of 3.5 mm. It is divided into two zones 

 quite clearly distinguished in opacity, the outer zone being due to the 

 abrupt thinning out of the fine granular matter of the disc. With a 

 liand-lens the region of the nucleus may be made out in the living egg 

 as a spot surrounded by a lighter ring or halo, the " fovea." The whole 

 affected area surrounding the nucleus is shown in Pig. 6a. The nucleus 



