2O 



R. W. HEGNER. 



deutoplasmic spaces. When the egg is deposited, the germinal 

 vesicle, has already moved, to a point near the ventral surface 

 just a trifle anterior to the center of the egg; here polar-body 

 formation takes place. One or more male nuclei are present near the 

 anterior end of the egg. Suspended in the " Keimhautblastem " 

 near the posterior end of the egg is a mass of deeply staining 

 granules which I have called the "pole-disc." These granules 

 occupy the inner portion of the peripheral cytoplasmic layer and 

 cover about one eighth of the area at this end of the egg (Fig. i). 

 Surrounding the egg are the vitelline membrane and the chprion. 

 After the conjugation of the sperm-nucleus with the egg- 

 nucleus, which occurs a few hours after the eggs are laid, the 



FIG. I. 



FIG. 2. 



Pd.g. 



FIG.3. 



FIG. 4. 



FIG. I. A portion of the posterior end of an egg of C. bigsbyana in longitudinal 

 section showing the arrangement of the pole-disc granules (pd-g)- ,V = yolk; khbl 

 - " Keimhautblastem." 



FIG. 2. Longitudinal section through the posterior end of an egg of C. bigsbyana 

 showing the primordial germ-cells (pc) containing pole-disc granules (pd-g}. 

 Nuclei which are prevented from forming blastoderm cells produce a pseudoblasto- 

 dermic syncytium (psbl}. The letters pc.c indicate the canal through which the 

 pole-cells later migrate into the embryo. bl= blastoderm. _y = yolk. 



FIG. 3. A single primordial germ-cell showing pole-disc granules (pd.g}. 



FIG. 4. Longitudinal section through the posterior end of the egg of C. lunata 

 described in Exp. 2a. The letter <t indicates where germ-cells would be found in an 

 uninjured egg. &/= blastoderm, y = yolk. 



cleavage nuclei increase rapidly in numbers and migrate in all 

 directions toward the periphery reaching the " Kleimhautblastem " 

 at the expiration of eighteen hours. Those nuclei (sixteen in 



