298 W. G. VanJVame — Emhryolociy of Eustt/locltus. 



Plate XXXVI. 



Fig. 1. — Young ovarian egg, showing the large germinal vesicle, the nuclear 

 reticulum and large nucleolus. Enlarged 860 diameters. 



Fig. 3. — Ripe egg in which the first polar spindle asters are visible, though they 

 do not show the centrosomes. Prejiaration stained Avith Delafield's haema- 

 toxylin. Most of one aster lies in another section. The nucleolus has dis- 

 appeared, and the beaded threads of chromatin have become conspicuous, 

 X 860. 



Figs. 3« and 36. — Sections of the same egg, which is in a later stage than fig. 2. 

 Shows the polar spindle centrosomes and the rounded chromosomes, one of 

 which in fig. 3a has already opened into a ring, x 860. 



Fig. 4. — Slightly later stage. Somewhat over-stained, so that the centrosomes 

 appear very large. Their elongated form indicates their approaching divi- 

 sion. X 860. 



P'ig. 5. — Uterine egg showing polar spindle and spermatozoon. The centrosomes 

 have already divided. The centrosphere has acqiiired a distinct outline. 

 x860. 



Fig. 6. — Spermatozoon (from an egg in the stage of fig. 5), one end of which is 

 surrounded by the dark area which is less distinctly seen in fig. 5. x 860. 



Fig. 7. — Recently laid egg. The polar spindle is still in a central position. The 

 sBprmatozoon has contracted into the shape of a spindle, x 860. 



Fig_ 8. — First polar spindle after it has reached the surface of the egg. This 

 specimen is unusual, as all the chromosomes still have the ring form. In 

 this stage some of the rings at least have usually broken, x 1240. 

 Note. — Figs. 5, 7 and 8, as well as some that follow, illustrate the separation 



of the derived centrosomes, which in this species generally occurs in a longitu- 

 dinal direction, parallel to the axis of the spindle or nearly so. 



Figs. 9 and 10. — Chromosomes of eggs in the same stage as fig. 8. x 1240. 



Plate XXXVII. 



Fig. 11. — First polar spindle, introduced to show the chromosomes, x 1240. 



Fie. 12. — Later stage of the first polar spindle. The centrosomes of the outer 

 pole of the spindle, which is somewhat over-stained, lie in an oblique 

 instead of the usual axial position. The centrosomes of the inner pole have 

 begun to separate, x 860. 



Fig. 13. — Formation of the first polar body, x 860. 



Figs. 14, 15, 16. — Three stages of the second polar spindle, showing the reduc- 

 tion of the aster rays in strength and number, and the formation of the new 

 spindle from the centrosphere. In the earliest of these (fig. 14), the chromo- 

 somes have already split into two segments. The chromosomes are more 

 widely separated from each other thsiu in the first polar spindle. Figs. 

 14 and 15 x 1240. Fig. 16 x 860. 



Plate XXXVIII. 



Fig. 17. — Final stage of the second polar spindle, showing the cell-plate. Most 

 of the second polar body is in the next section. The chromosomes liave 

 swelled up into vesicles, x 1240. 



