SUMMARY OF PRINCIPAL RESULTS. 67 



IX. SUMMARY OF THE PRINCIPAL RESULTS IN THE STUDY OF 

 THE MATURATION OF THE EGG OF THE MOUSE. 



1. Parturition occurs at any time during the 24 hours of a day, but 

 more frequently in the early morning. 



2. The stages of the formation of the first spindle, the division of the 

 first spindle, the formation of the second spindle, and the division of the 

 second spindle are relatively, and probably absolutely, very short. 



3. The whole maturation process requires not less than 4 nor more 

 than 15 hours. 



4. Maturation usually occurs at some time during the period ex- 

 tending from 13! to 28 J hours after parturition. 



5. Ovulation may occur at any time during a period beginning at 

 14^ and ending at 28^ hours after parturition. 



6. Ovulation may occasionally take place in the stage of the first 

 spindle, sometimes during that of the telophase of the first spindle and 

 the formation of the second polar cell, but usually not till the egg con- 

 tains the second spindle. 



7. Insemination is most successful when it occurs between the i8th 

 and 3oth hours after parturition. 



8. The spermatozoa reach the egg in from 4 to 7 hours, or more, 

 after insemination. 



9. The pronuclei are formed probably within a few minutes after 

 the penetration of the spermatozoon. 



i o. The diameter of the egg decreases from the stage of the germina- 

 tive vesicle until it reaches the oviduct, when it increases slightly. 



1 1 . The chromosomes of the first spindle are formed from the chro- 

 matin of the germinative vesicle, and possibly also from the wall of the 

 nucleolus. 



12. They are formed before the nuclear membrane disappears. 



13. They show indications of both transverse and longitudinal divi- 

 sions, and are therefore "tetrads." 



14. In the first maturation division the tetrads divide transversely. 



15. All first spindles divide. 



1 6. The spindle fibers are probably derived in part from the nu- 

 cleolus. 



17. The chromosomes of the second spindle are " dyads" and divide 

 longitudinally, separating along a plane which is probably identical with 

 the longitudinal division-plane of the tetrads. 



1 8. The chromosomes of each spindle number twenty. 



19. Typical centrosomes are wanting in both spindle figures. 



20. Bodies surrounding the poles of the spindles, here called cir- 

 cumpolar bodies, and the clear region surrounding the spindle are char- 

 acteristic of morphologically active stages of the spindle. 



