MUNSON: SPERMATOGENESIS OF PAPILIO. 
93 
between the centrosome and nebenkern, causing these bodies to 
approach each other. In plate 13, figure 39a, are seen traces of the 
original mantle fibers of the second maturation spindle, the central 
spindle having condensed, as described, into a nebenkern. The 
nucleus is here already expanded and its eccentricity caused by this 
expansion is also evident. Compare, also, the other spermatids in 
this cyst (pi. 13, fig. 39) with those in figure 39a. It is here seen that 
the nebenkern, nucleus, and centrosome rarely lie in the same axis. 
Writers who have observed this almost invariably attribute the effect 
to movement of the centrosome, the latter being described as changing 
its position and moving around the nucleus till it ultimately is thought 
to become permanently located between the nebenkern and nucleus 
or even to become imbedded in the nebenkern. I shall show that 
that is not true in this case; for as the spermatid elongates into the 
spermatozoon, the nucleus becomes again crowded in between the 
centrosome and the nebenkern, and the three bodies — centrosome, 
nucleus, and nebenkern — all assume their fixed position in the long 
axis of the growing spermatozoon in the order named (pi. 14, figs. 
40, 46). Thus the centrosome finally becomes located at the head 
pole of the nucleus, the nebenkern invariably at its tail pole. This 
is just what could be predicted from the relation of the three at the 
close of the second maturation division. 
Accidental bodies .— The subject of spermatogenesis has been unnec¬ 
essarily complicated by writers who describe two or three other 
bodies under special names such as mitosome, acrosome, and 
chromophile bodies. In a very few instances I have seen in the 
neighborhood of the nucleus a minute archoplasmic body resembling 
a second smaller nebenkern (pi. 17, figs. 133, 134). But I interpret 
it either as a slight remnant of the first maturation spindle, owing 
its persistence perhaps to a stray chromatin granule accidentally left 
behind in the first mitosis, or as a condensed remnant of the astral 
/ 
rays or archoplasm of the centrosome. I have also seen a small 
body resembling a centrosome in the neighborhood of the nebenkern 
(pi. 17, figs. 128, 130), which led me to believe that the centrosome 
divides, one centrosome taking its position at the head pole of the 
nucleus, the other at the tail pole. A somewhat similar body is also 
occasionally seen inside the nebenkern. I regard these now as frag¬ 
ments of chromatin left behind in the last maturation spindle, which 
either become imbedded in the nebenkern as it forms, or are left just 
