424 
Charles Lincoln Edwards 
and leaves the possibility of its being a sex-determinant “unsettled for 
the present”. 
However in an appendix to Miss Borixg’s paper, Boveri (1909) 
comes to the positive conclnsion that this small chromosome in Ascaris 
ynegalocephala is sex-prodncing, and also reports the finding by himself 
and Gülick in Heteralis of an idiochromosome of the same general 
character as the type III {Protenor, Anasa etc.) of Wilsox (1909). 
In the maturation divisions of the spermatogenesis of Ascaris megalo- 
cephaJa. wliich have been accurately investigated by 0. Hertwig (1890) 
and Brauer (1893) and also by Borixg (1909) nothing has been observed 
hitherto of an independent chromatin element that conld be interpreted 
as an idiochromosome. Boveri (1909) has offered as an explanation for 
this condition, that the odd chromosome here may be nnited with one of 
the large chromosomes. Studying a great nnmber of males, I have found 
in one lot of forty-five from one horse, two individnals, worms A and B, 
in which an idiochromosome can be followed thronghont the whole ma- 
tnration period, and another, worin C, from which unfortimately the divi- 
sion section was lost bnt which shows the idiochromosome in the primary 
spermatocytes (pl. XXI, fig. 4). 
In the equatorial plate of the spermatogonial divisions (pl. XXI, fig. 1), 
the impaired idiochromosome is present, as is also shown by Borixg (1909), 
(pl. X, fig. 14). In the vesicular niicleus of the growth period of the 
priniaiy spermatocytes each of the large chromosomes is composed of 
four weil separated rods, as described by Hertwig (1890), and siniilar 
Io those given as “pathological” by Brauer (1893) (pl. XI, figs. 105 — 107). 
At this time the idiochromosome in worm A is composed of halves in the 
form of two short rods lying to one side of the two developing tetrads 
(pl. XXI, fig. 2). In worm B the idiochromosome is distinctly divided 
(pl. XXI, fig. 5). bnt the halves are not separated as in worin A. In prepara- 
tion for the first maturation division the rods of the tetrads shorten and 
thicken (pl. XXI, figs. 3 — 6). As. the spindle fornis, the tetrads divide, with 
the connected halves of the idiochromosome forrning a line between them 
(pl. XXI, fig. 7). The halves of the idiochromosome are joined to each 
other and at their ends to one of the dyads of each migrating gronp of 
chromosomes (pl. XXI, fig, 8), by protoplasmic processes which extend as 
niitosis proceeds. In some cases, when the cells have been pressed apart 
linder the cover-glass, the protoplasmic processes are elongated, still main- 
taining their Connections (pl. XXI, fig. 11). The halves of the idiochromo- 
sonie separate as the cell constricts (pl. XXI, figs. 9 — 10), iintil finally, when 
the division of the cytoplasm is completed, the interconneeting proto- 
