234 



B YRNES. 



EXPLANATION OF PLATE XL 



All figures drawn with camera and lenses of Zeiss. Honiogetieous immersion, 

 /.J mm. apochromatic compensation, ocular 4. 



Fig. I. Section of ovarian egg containing small astrosphaere. 



Fig. 2. Section of ovarian egg containing a well-formed archiamphiaster. 

 The centrosphere of the aster consists of two zones, a dark " cortical " zone and 

 alight "medullary" zone. The "medullary" zone contains two oblong centro- 

 somes composed of granules. 



Fig. 3. Section of egg just deposited. The egg contains an archiamphiaster 

 similar to that in the ovarian egg. In the " cortical " zone to the left of the 

 spindle the central granules are arranged irregularly. In the "cortical" zone to 

 the right the central granules are arranged in two groups. 



Fig. 4. Section through one pole of the archiamphiaster. The centrosphere 

 consists of four concentric rings. The central granules are grouped so as to form 

 two dumb-bell-shaped centrosomes. The sperm-head is seen at the lower pole. 



Fig. 5. Section through pole of archiamphiaster. No centrosomes are 

 present. 



Fig. 6. Centrosphere and centrosomes of archiamphiaster. 



Fig. 7. First maturation spindle. Sperm with deeply staining body at lower 

 pole of egg. 



Fig. 8. Formation of first polar body. The central centrosphere is enlarging 

 before the separation of the polar body. Sperm-head vesicular. 



Fig. 9. Extrusion of first polar body. Centrospheres in the archiamphiaster 

 stage. 



Fig. 10. Section through egg-astrosphaere after extrusion of first polar body. 

 The centrosphere is beginning to enlarge. The centrosomes are single granules 

 which are beginning to separate. 



Fig. i I . Section through egg-astrosphaere after extrusion of first polar body. 

 Beginning of the disappearance of the " cortical " and " medullary " zones. 



Figs. 12 and 13. Later stages than Fig. 11. 



Fig. 14 a, b, c. Three successive stages through the centrosphere just before 

 the second maturation spindle begins to form. 



Fig. 15. Early stage in the formation of the second maturation spindle within 

 the centrosphere. The astral rays still persist. The chromatin lies on the 

 periphery of the sphaere where it was left after the extrusion of the first polar 

 body. 



Fig. 16. A later stage in the formation of the second maturation spindle. 

 The spindle still lies within the centrosphere, which is outlined by granular thick- 

 enings in which the rays of the old aster terminate. 



Fig. 17. The second maturation spindle after the disappearance of the cen- 

 trosphere. Chromatin on the upper surface of the spindle. 



Fig. i8. Later stage than Fig. 17. 



Fig. 19. Second maturation spindle. 



Fig. 20 a. Section through pole of second maturation spindle. 



Fig. 20 b and b'. Sperm-asters in the same egg. 



Fig. 20 c. Sperm accompanying sperm-asters. (Fig. 20 b and b'^ 



