CYTOPLASMIC INCLUSIONS OP THE GERM-CELLS. 433 
fig. 13 ifc is below the nucleus, in PL 23, fig. 16 it is above, 
and in Pl. 23, fig. 14 it is at the side, assuming that the thick 
line represents the head end of a sperm (see Pl. 23, fig. 17). 
The mitochondria have by now run together to form the large 
mitosome (or “ nebenkern”) of Platner, or the macromitosome 
under my nomenclature, and the nucleus moves up near the 
wall of the sperm cyst wall (PL 23, figs. 14 and 16). The 
micromitosome leaves whatever position it hitherto occupied, 
and becomes placed between the nucleus and the macromi- 
tosomal spireme, as shown in Pl. 23, fig. 17, and in the figures 
in PL 25. 
Its further history is not at all easy to follow out, for the 
sperm begins to lengthen and thin out, and the frequent 
presence of several acrosome bodies contributes to the 
confusion. 
Though I was unable to make any smears of testes of 
Smerinthus, examination of such preparations from other 
species leads me to doubt whether the micromitosome always 
divides. I have examined a very large number of spermatids, 
and a few of them do not appear to possess this body ; more- 
over, it seems that the size of the micromitosome is seldom 
very regular. In some cases, especially in Vanessa, this 
becomes very apparent on examining the spermatids smeared 
from a single nest of cells. One counts four or five spermatids 
with micromitosomata, and then often finds two or three quite 
near in which no such body can be found. All of such 
cases are not due to the micromitosome being hidden by the 
macromitosome or by the nucleus. I would not feel justified 
in stating that the micromitosome of one spermatid whose 
immediate neighbour had no such body was twice as big 
as the micromitosomes from a group of cells all of which 
possessed the body. In Smerinthus I can say that on the whole 
the micromitosomes are remarkably uniform in size and in 
the constancy of their presence in the developing spermato- 
zoon. In such a form as Euchelia I could not find a micro- 
mitosome in any spermatogonial divisions or rest stages, and 
it was not until the growth-period had begun that this body 
