BILATERALITY OF THE PIGEON's EGG 277 



It should be borne in mind in this discussion that the facts are 

 presented in the order opposite to that in which the analysis was 

 made and so apparently trivial differences in the youngest oocytes 

 fit into a general scheme of development and become quite appre- 

 ciable during the cell's linear growth of 700 diameters. 



IV. THE OVARIAN HISTORY 



Most workers on the bird's ovary have divided the ovarian 

 development into more or less clearly defined periods, usually on 

 the basis of the nuclear phenomena alone. The best of these 

 analyses are those of D' Hollander ('04) for the embryonic stages 

 and of Sonnenbrodt ('08) for the subsequent growth periods. The 

 classification that has been made here is based upon the phases of 

 physiological activity of the oocyte as a whole, i.e., the four periods 

 described are distinguished by the different forms in which the 

 cell organization is manifested. 



The primordial follicles, the youngest oocytes found in the 

 adult ovary, form the starting point in this discussion. They are 

 in practically the same stage of development as the oldest oocytes 

 of a chick two weeks after hatching or a pigeon several weeks 

 older, and they may be considered as the final stages of the first 

 period of growth after the differentiation of the oocyte as such. 

 This period, in the case of the primordial follicles, involves a slow 

 increase in size from 10 to SO/t and the accumulation of deutoplasm 

 in the form of lipoid spherules. It corresponds to Sonnenbrodt's 

 period V, in which the chromosomes stain deeply and have a 

 characteristic thickened form. 



A . The primordial follicle: (oocytes to 0.09 mm.) 



The form relations of the primordial follicles can be studied 

 satisfactorily only in the fresh condition and the following de- 

 scription is based primarily on the study of material dissected out 

 of the living ovary in salt solution, usually stained intra vitam and 

 examined with a 3 mm. Zeiss aDochromat immersion lens. The 

 cover slip was so supported that the oocytes were not subjected 



JOURNAL OF MORPHOLOGY, VOL. 23, NO. 2 



