294 



Summary of Results. 



I. The accessory chromosome appears in the resting stage of the 

 secondary spermatogonia as a chromatin nucleolus characteristically 

 close to the nuclear wall. 



II. At the last spermatogonial division it passes over into the 

 resting stage of the primary spermatocyte without entering a reticular 

 stage as do the ordinary chromosomes. 



III. Both the primary and secondary spermatogonia have a meta- 

 phase group of 35 chromosomes, 



IV. Metaphase groups of follicle cells of the ovary contain 36 

 chromosomes. 



V. Synapsis occurs in the early stages of the growth period by 

 an end to end union of pairs of univalent elements. 



VI. Equatorial plates of primary spermatocytes contain 18 chromo- 

 somes. 



VII. The accessory chromosome passes undivided to one pole of 

 the first maturation spindle and thus produces a dimorphism of the 

 daughter cells and the resulting spermatozoa. 



VIII. The first maturation division is reductional; the second is 

 equational. 



IX. Equatorial plates of secondary spermatocytes show a disparity 

 in the number of chromosomes; one group contains a large U-shaped 

 element peripherally and numbers 18; those groups lacking a body of 

 such form contain only 17 chromosomes. 



X. The accessory chromosome can be traced as a specific structure 

 from the resting stage of the last order of spermatogonia through all 

 the various phases of synapsis and maturation until it disintegrates in 

 the head of the ripening spermatozoa. 



Literature cited. 



Bateson, W., '07, Facts limiting the theory of Heredity. Science, Vol. 26, 



No. 672, p. 649. 

 Castle, W. E., '03, The Heredity of Sex. Bull. Mus. of Comp. Zoöl. 



Harvard, Vol. 40, p. 189. 

 Henking, H., '90, Ueber Spermatogenese und deren Beziehung zur Ei- 



entwickelung bei Pyrrhocoris apterus. Zeitschr. f. wissensch. Zool., 



Bd. 5], p. 685. 

 Mo Clung, C. E., '02, Accessory Chromosome — Sex Determinant? Biol. 



Bull., Vol. 3, p. 43. 

 Montgomery, J. H., '04, Some Observations and Considerations on the 



Maturation Phenomena of Germ Cells. Biol. Bull., Vol. 6, p. 137. 



