370 K. MASUI: 
IX. General Consideration. 
A. THE Accessory CHROMOSOME. 
An odd or unpaired chromosome also exists in the male gerin cells of 
the horse as in many other animals. Its form and behavior correspond 
almost exactly with the body termed by Wıusox the heterotropie or accessory 
chromosome, so that I do not hesitate to identify it with the same. The 
accessory chromosome, however, can not be recognized during the division of 
the spermatogonia ; it probably divides into two like the ordinary chromo- 
somes, but comes in view during all succeeding stages. During the prophase 
of the first maturation division, it is situated outside the chromosomes, as an 
oval body, but sometimes it presents a rod or heart-shape, or rarely bipartited 
form, and during the division it passes undivided to one pole of the spindle 
in advance of the ordinary chromosomes. In the cells of the secondary 
spermatocytes in which it is present it assumes the form of a chromosome 
nucleolus, and divides into two like the ordinary chromosomes, to enter into 
the two daughter cells, but it can not be traced in the spermatid. The 
oceurrence of an accessory chromosome in vertebrates, as I am aware, was 
first recorded by GuyrER in the guinea-fowl (’09), in the domestic fowl 
(09), and in man (10). This was soon followed by Jorpan (11) who 
found the same in the opossum, STEVENS (’11) in the guinea-pig, WODSEDALEK in 
the pig (13) and in the horse (14), BAcHHUBER in the rabbit (16) and Yocom 
(17) in the mouse. All these investigators, with the exception of GUYER in the 
common fowl ('16), believe that both classes of spermatids, the one with an 
accessory chromosome and the other without it, develop into spermatozoa. 
WODSEDALER (713) found two accessory chromosomes in the male germ 
cells of the pig and was convinced of the existence of dimorphism among the 
spermatozoa, the one with and the other without the accessory, and by careful 
examination of the male and female somatic cells of the embryo he also found 
the existence of a dimorphism in the number of chromosomes in these cells, 
from which he concludes that “the result of the present investigation 
(his investigation), therefore, adds support to the chromosome theory of- sex- 
tarminat: 2 i . . - 
determination, since they shew that in the vertebrates, as well as in some of 
