OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 579 



6. The mature ootid contains eighteen dyad chromosomes, 

 which unite with the twelve or eighteen dyads of the sperm nu- 

 cleus to form respectively: — (a) a zygote (male individual) wdth 

 thirty dyad chromosomes, or (b) a zygote (female individual) 

 with thirty-six dyads. 



7. Neither maturation division takes place before insemina- 

 tion, that is the penetration of a spermatozoon. 



8. There is a definite interkinetic period between the two 

 maturation divisions during which a nuclear membrane is formed. 



9. The cleavage centrosomes are traceable directly, through 

 the one brought in by the sperm, to the centrosome that arose 

 with the spermatid. 



10. Fertilization is possible from the time that the sperm en- 

 ters the egg, up to the time of the reorganization of the nuclei 

 of the first two cleavage cells and the final union of the male 

 and female chromosomes. 



11. Of the five soma cells immediately derived from the stem- 

 cell series, all except the first one undergo 'diminution' at their 

 first division; the first soma cell also does in fifty per cent of the 

 individuals, but in the remaining fifty per cent the division is 

 deferred until the division of its daughter cells. 



12. The descendants of the sixth generation of the stem-cell 

 series are entirely propagational in nature. 



13. The Querkerbe, always present, at least potentially, in all 

 the chromosomes of the stem and propagation cells, disappears 

 entirely in the chromosomes of the soma cells after ' diminution' 

 has occurred. The Querkerbe is probably the sign of a plurival- 

 ent condition of the chromosome, and never indicates the plane 

 of a syndetic union or that of a maturation division. 



