426 
Charles Lincoln Edwards 
As tlie equatorial plate for the first maturation division is formed, the 
five idiochromosomes are drawn into the midst of the ordinary chromo- 
somes (pl. XXII, fig. 25). In the metaphase of the first dmsion the idio- 
chromosome pentad group lies in the center of the nineteen bivalent 
chroniosomes (pl. XXII, fig. 26). As the two sets of nineteen chroinosomes 
separate, the five univalent idiochromosomes are suspended in a group 
between them (pl. XXII. fig. 27). Each daughter group of nineteen chro- 
mosomes proceeds pölarwards in the form of a somewhat irregulär 
double ring (pl. XXII, figs. 28 — 29 a, c), vhile in the lagging heterotropic 
pentad (pl. XXII, figs. 30 — 31) often one element is the larger and joined to 
its own polar group by a protoplasmic thread (pl. XXII, fig. 30). However 
one element is not constantly the larger, and consequently we cannot 
subdivide the pentad into two classes of idiochromosomes. In the ana- 
phase this pentad element is drawn into the midst of the nineteen ordi- 
nary chroniosomes (pl. XXII, figs. 31 — 32), so that at the end of the first 
division there are two kinds of secondary spermatoc tes, one with simply 
nineteen chromosomes and the other wdth nineteen chromosomes plus the 
five heterotropic idiochromosomes. 
Düring the second maturation diiision the differentiated secondary 
spermatocytes divide equationally, producing sister cells, one dass pair with 
twenty-four chromosomes, including the five idiochromosomes (pl. XXII, 
fig. 33), and the other pair with nineteen ordinary chromosomes (pl. XXII, 
fig. 34). In the further development of the spermatids the chromosomes 
at first form a crescentic group, with the homs gradually closing together 
to an incomplete ring, accompanied by an increasingly closer approxima- 
tion of the chromosomes (pl. XXII, figs. 35 — 38). Within the ring of nineteen 
elements the idiochromosome pentad group is plainly to be seen (pl. XXII, 
figs. 35 — 36). 
In agreement with Boveri (1887), Carxoy (1887) and Fürst (1898) 
(pl. IX, fig. 35), I find twenty-four chromosomes in the equatorial plates 
of the first and second maturation divisions of the egg (pl. XXII, fig. 39). 
In accord with Wilsox’s theory, in each of these groups there are probably 
five idiochromosomes although I have not found them especially distin- 
guishable. Hence the fertilization of the egg by a Spermatozoon having 
twenty-four chromosomes produces a female with forty-eight chromo- 
somes, including two idiochromosome pentad groups, and by a Spermato- 
zoon having nineteen chromosomes, a male with forty-three chromosomes, 
including one idiochromosome pentad group (pl. XXII, fig. 23). Boxxevie 
(1901) gives forty-eight to fifty chromosomes as the average result of a 
series of counts of these elements in the first cleavage spindle. This per- 
