DAVIS: SPERMATOGENESIS. LIS 
tid. ‘The further changes consist chiefly in a still greater elongation 
of the head until it becomes several times the length shown in Figure 
- 223 and correspondingly smaller in diameter. 
Spermatids which are much larger than normal ones and contain 
two or more centrosomes are occasionally met with. Figure 217 
shows one of these abnormal spermatids with four centrosomes, each 
of which has an axial filament connected with it. ‘The number of 
such abnormal spermatids varies in different individuals, although 
they are never very common. Similar abnormal spermatids have 
been described by Paulmier (99) and others. 
I have not found evidence of the degeneration of spermatids or 
spermatozoa, except in rare cases. 
Inasmuch as only one-half of the spermatids contain the monosome, 
and as there is no evidence that the monosome is extruded from the 
nucleus during the metamorphosis or that any considerable number 
of the spermatids degenerate, it follows that the mature spermatozoa 
are dimorphic, even though there is no recognizable difference between 
them,— half of them containing the substance of the monosome, the 
other half being without that substance. 
B. Steiroxys trilineata. 
In the resting spermatids (Plate 8, Figs. 200-203) the autosomes. 
have become broken down into granules distributed through the nu- 
cleus, but the monosome retains its compact form and shows the 
staining reactions characteristic of dividing chromosomes. It forms 
a lenticular body closely applied to the inner surface of the nuclear 
membrane and, on account of its large size and staining reactions, is a 
very conspicuous element of the spermatids. Figures 200 and 202 
show resting spermatids which contain the monosome, while Figures 
201 and 203 show others in the same stage in which this element is 
lacking. Lying near the nucleus, on the side covered with the greatest 
amount of cytoplasm, is a rounded homogeneous body staining deeply 
with Bordeaux; for convenience I shall call this the Nebenkern, with- 
out implying anything in regard to its homologies. Often a less 
deeply staining body can be distinguished closely applied to the nu- 
clear membrane near the Nebenkern (Fig. 203). ‘This body is usually 
difficult to distinguish from the surrounding cytoplasm, but is prob- 
ably of universal occurrence. During the telophase of the second 
maturation division the cytoplasmic structures are very indistinct, so. 
that I have been unable to determine the origin of the Nebenkern and 
