438 
J. BRONlA GATENBY. 
organ, therefore, according to this suggestion, is an 
arrangement for enabling the filament to grow at both ends, 
the centrosome end undoubtedly assisting also ; it is possible 
that the terminal body ( T.B .) is in reality a part of the centro- 
some, detached and carried out on the tip of the filament in 
order to assist growth at the opposite end. The dark terminal 
dot is the growing tip, the clavate organ the storehouse of 
food matter. 
The Acroblasts and Acrosome ( Smerinthus) . * 
After the individual mitochondrial bodies have become 
clearly visible, one notices other more darkly staining, slightly 
curved, sickle-shaped bodies, much less numerous and more 
definitely located. These structures are much denser than 
the mitochondria, as is shown by their staining reactions with 
iron hsematoxylin. At the end of the growth period these 
darker bodies appear to have some relationship with the 
nucleus ; the mitochondrial bodies may be scattered irregu- 
larly, but the darker bodies, which, I believe, form the 
acrosome of the sperm, are placed generally with their concave 
surface towards the nucleus. Moreover, they nearly always 
occupy the spaces clear of mitochondrial bodies (see PL 23, 
fig. 8, A. B., 9, 10, 12, and 13). 
When the maturation divisions take place, the acroblasts, 
as they may be called, are even more definite in their 
behaviour. They are almost invariably placed in a semi- 
circular figure near the aster, as is shown in PL 23, figs. 9 and 
10, PL 25, figs. 32, 33, 43, and 48. 
In some cases the acroblast, which looks solid for most of 
the growth period, is seen to be vesicular, only one side of the 
vesicle is always more solid than the other. This is shown in 
Text-fig. 2, 5. 
The acroblasts are never quite equal in size, but the largest 
ones are seemingly formed by the running together end to 
end of two acroblasts. The latter, when not vesiculiform, are 
more darkly staining than when they are hemispherical. In 
