MUNSON: SPERMATOGENESIS OF PAPILIO. 
89 
plasm also looks normal. The two nuclei are probably not the result 
of amitosis, but unusual cases of failure on the part of the cytoplasm 
to constrict after the anaphase of mitosis. Mention has already been 
made of those cases in maturation, where the second division has 
begun before the first is completed and where the two spermatocytes 
second order differ as to the time in which they prepare for the final 
division. Normally all cells in a cyst, whether spermatogonia or 
spermatocytes, are found in almost identical phases of mitosis (com¬ 
pare fig. 24-32, pi. 13). But there are not a few exceptions, and 
these have been of great service in determining the sequence of events 
(compare fig. 29 and fig. 34, pi. 13). These are, it must be admitted, 
exceptions, but there is no reason to suspect that their presence indi¬ 
cates pathological material. 
Occasionally a spermatid also with two nuclei has been found (pi. 
17, fig. 124). It is not absolutely certain that one of the two bodies 
is not an enlarged centrosome. 
The giant spermatids show no trace of these abnormal features. 
Their great size offers special opportunity to study their structures 
and their transformation into spermatozoa (pi. 13, figs. 39, 39a; pi. 
16, fig. 119-121; pi. 17, fig. 131; compare these with pi. 17, fig. 
126-130). 
After the last maturation division, the resulting spermatid can be 
identified by the presence, in the cytoplasm, near the nucleus, of a 
large spherical body, the so called nebenkern. 
While the large cytocysts are hollow spheres, with the spermato¬ 
cytes arranged in a single layer around the periphery, the spermato- 
cysts have cells also in the interior of the cyst (pi. 13, figs. 39, 39a). 
I have already shown that, in the first maturation division, the 
spindle is always so placed as to lie in the short axis of the cell and 
consequently parallel to its base. This results in an equal division 
of the cell (pi. 13, figs. 36, 38). 
But in the second maturation division no such relation of the spindle 
exists. The second division often results in the production of one 
cell related to the cyst wall, and another occupying the hollow cavity 
of the cyst (pi. 13, figs. 39, 39a). Those in the lumen are usually 
spherical, while those in relation with the cyst wall are compressed 
laterally and of course flattened at the base (pi. 13, fig. 39a). 
Origin of the nebenkern .-— Owing to the fact that, at the end of the 
first maturation division, the nucleus is not entirely reconstructed 
