238 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



nucleus contains a large, spherical, sharply defined nucleolus, surrounded 

 by a granular layer which is continuous with a network of threads 

 ending around the surface of the nucleus in a sharply defined granular 

 border, quite different from the surrounding yolk. In the next stage 

 which I found, Fig. 2, the egg is apparently in the act of fertilization. 

 The yolk has shrunken away from the follicle a little, so that its own 

 outline can be distinguished from the outline of the inner ends of the 

 follicle cells with which it was in immediate contact at the preceding 

 stage. At the upper end of the yolk, where the space between it and the 

 follicle is greatest, is a deeply stained rod-like body which is probably 

 the spermatozoon. The outline of the nucleus is vague and indefinite, 

 the nucleolus and the network are no longer visible, and in their place 

 near the center of the nucleus there are two faintly defined groups of 

 minute granules. This section, Fig. 2, is like Fig. 1, transverse to the 

 length of the fertilizing duct, and the spermatozoon is shown by the 

 study of the series to be near the proximal surface of the egg, or that 

 surface which is nearest the upper end of Fig. 10. It will be seen that 

 the spermatozoon is in the middle plane of the egg, and a comparison of 

 Figs. 1, 2 and 10 will show that as the spermatozoa pass through the 

 fertilizing duct they must meet each egg at approximately the same 

 point, on the middle line of the proximal surface. The follicle at this 

 stage is quite different from Fig. 1. It is much thicker, the cell bound- 

 aries are much less sharp, and there is a great increase of follicular 

 nuclei, and a change in their shape and general appearance. They are 

 no longer round, but elongated in radial lines, their granules are larger 

 and less numerous, and here and there in every section is a nucleus in 

 some stage of division. These dividing nuclei are always near the inner 

 border of the follicle, as shown in Figs. 2 and 3. 



SECTION 3. Segmentation. 



Successive stages of segmentation are shown in Fig. 3 of Plate X, 

 in Figs. 1 to 10 of Plate IX, in Fig. 11 of Plate IX, in Figs. 4 and 5 of 

 Plate X, and in Figs. 6, 7 and 8 of Plate X. 



Plate X, Fig. 3 is a section from a series through an egg which has 

 undergone its first division, cut in a plane parallel to the oviduct, or at 

 right angles to Figs. 1 and 2. The egg is divided in the plane of the 

 paper into two cells ; one of them with a nuclear figure which shows that 

 it is about to divide into an upper and a lower portion. On the proximal 



