90 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
before the second division to form spermatids begins, the second 
spindle differs markedly from the first as regards its origin. It has 
already been pointed out that, whereas in the first maturation spindle, 
(derived wholly from the nucleus) each spindle fiber is connected with 
a distinct chromosome, in the second division, the spindle consists 
of a peripheral portion, whose fibers have no connection with chromo¬ 
somes, and a central portion to which the chromosomes are attached. 
I believe these two parts of the spindle have different origins; the 
outer “mantle fibers,” being derived from the persistent intermediate 
fibers of the first spindle, while the central spindle is derived, partly 
at least, from the chromosomes. As there are now only fourteen 
chromosome segments to be drawn to each pole, only a corresponding 
number of spindle fibers with chromosomes is formed (compare pi. 
16, fig. Ill with fig. 117). 
This difference in the outer and inner part of the second maturation 
spindle becomes manifest in the peculiar behavior of the intermediate 
fibers of this spindle before and after the final completion of the last 
division. Before the final separation of the two spermatids (pi. 16, 
fig. 118), the outer portion of the spindle melts away by breaking up 
into granules. The central fibers persist till the final constriction of 
the cytoplasm (pi. 16, fig. 118). As the final constriction of the 
intermediate fibers occurs, the central fibers contract and withdraw 
into the center of the cell. Here they form a homogeneous archo- 
plasm-like body close to the chromosomes which have not, as yet, 
expanded into a new nucleus (pi. 16, fig. 119). The outer granular 
remnant of the mantle fibers now forms a ring around the central 
archoplasmic portion, as the cytoplasm closes in at the place of con¬ 
striction (pi. 16, fig. 119). This concentric striation of the contracted 
spindle, now the “nebenkern,” gradually disappears as the central 
portion assumes more and more the character and appearance of the 
outer layers. 
The resistance of the maturation spindles to reagents is remarkable. 
In studying the living dividing cells on the slide, I have seen the cyto¬ 
plasm gradually disintegrate, become vacuolated, and disappear while 
the spindles remained as perfect as ever. In testing the effects of 
reagents, too, I have been able to dissolve practically the whole of 
the cytoplasm of all the cells of the cyst, while the spindles remained, 
showing a system of connected spindles throughout the whole cyst. 
In the case of the second maturation spindle which is transformed 
