CYTOPLASMIC INCLUSIONS OF THE OERM-CELLS. 437 
to the original description. As has been said, the advent of 
the centrosome, or centrosomes (if the division has taken 
place), at the edge of the cell (PI. 23, figs. 5 and 6) heralds 
the appearance of 4 the first cell processes. If the centrosome 
has not already divided it now does so, and from these two 
bodies there begins , to grow out flagella, two from each. In 
Pieris, Smerinthus, arid Spilosoma at least, the outgrowing 
flagella bear at their tips a remarkably large clavate structure 
of a definite size. In PI. 25, fig. 44, these organs are seen 
just as they begin to protrude from the surface of the sperma- 
tocyte. The club-like end is, as far as I am able to ascertain, 
not one of the cell processes carried out in a simple manner 
by the growing flagellum, but really a definite organ formed 
on and around the end of the filament. The very tip of the 
outgrowing flagellum is occupied by a dark spot, at this stage 
quite as darkly staining as the centrosome itself, and the area 
of the filament between the clavate end and the centrosome 
stains fairly densely. The filament can be seen passing 
through the substance of the clubbed end, as shown in PI. 25, 
fig. 50, which is drawn at a later stage when the club-shaped 
organ is at its largest. The terminal body ( T.B . ), the coarse, 
curiously vacuolated protoplasm of the clavate end (P.R.), 
and the central vacuole often present ( V.P.R .) are shown in 
this figure ; the filament ( F .) is seen to pass through the 
clavate organ and to end in the terminal body ( T.B . ). 
Reference may be made to PI. 24, figs. 19, 22, and 24, for 
this clavate flagellum. In PL 24, fig. 24 (Orgyia), the terminal 
club-like organ is small. In Spilosoma it is relatively huge. 
By the time the second maturation division has occurred the 
clavate end of the flagellum is smaller, and rapidly dwindles 
during spermatozoon formation, When the spermatozoon is 
at the stage of PI. 24, fig. 20, the clavate end is difficult to 
find. I believe that the terminal organ is really a store of 
nutritive matter, the terminal bodj a centre of metabolism 
for this matter; therefore the dwindling of the clavate end, 
and the later disappearance of the terminal body may be 
correlated with the growth of the flagellum. The clavate 
