GERM CELLS IN ASCARIS INCURVA 89 



SUMMARY AND CONCLUSION 



1. There is present in Ascaris incurva a sex chromosome com- 

 plex consisting of 8 X-chromosomes and one Y-chromosome, 

 which is mated by a definite component of the X-group. 



2. The cycle of the chromosomes may be represented by the 

 formulae : 



Spermatozoa Egg Zygote 



13A + 8X + 13A + 8X = 26A + 16X = 42 (female) 



13 A + Y + 13 A + 8X = 26 A + 8X + Y = 35 (male) 



3. The elements of the X-group appear to be mutually in- 

 dependent except during the reduction division. 



4. The X-chromosomes are carried to one pole in the reduc- 

 tion division on account of their attachment to one member 

 of a bivalent chromosome unit consisting of the Y-chromosome 

 and its mate among the X-components; otherwise these elements 

 are equally affected by the opposing forces acting during the 

 first phase of the mitotic division. 



5. The heterotypic mitosis may be divided into two phases; 

 one characterized by action of equal and opposite forces from 

 the spindle pole, the second characterized by an apparent cessa- 

 tion of the forces and movements probably due to cytoplasmic 

 currents. 



6. Measurement of volumes of nuclei of spermatozoa gives 

 a bimodal curve and the ratio between the volumes of nuclei 

 of the modal classes is closely proportional to the ratio between 

 the numbers of chromosomes contributed respectively to the 

 male producing and female producing spermatozoa. 



7. The X-chromatin is indistinguishable from other chromatin 

 during the growth stages. 



8. The growth stages present a seriation comparable with 

 that of other forms and therefore Ascaris need not be considered 

 as a case exceptional among animals in regard to the interpreta- 

 tion of the nature of reduction. 



9. Paired bodies resembling 'pro-chromosomes' are found 

 during the presynaptic stages, which transfonn during lepto- 



