SPERMATOGENESIS IN AMPHIBIA AND INSECTS 9 
blast, exactly as in Hemiptera. ‘This lies at first in the angle 
between nucleus and nebenkern, whence it moves to an anterior 
position (fig. 30). Later it appears again at the base of the 
head (figs. 31 and 34), so that it probably undergoes a migration 
similar to that which occurs in Hemiptera. The acroblast in 
this beetle impregnates in a very peculiar manner. Instead of 
forming a thimble-shaped mass with a heavily impregnated 
periphery as in the pentatomids (Bowen, ’20), it is apparently 
shaped like a disc, only the periphery of which is blackened by 
osmic acid. That this is a ring, not an optical section of some 
solid surface, is easily demonstrated by viewing the acroblast 
from different angles (compare figs. 30 and 31). 
From the acroblast the acrosome arises by a process of dif- 
ferentiation similar in all probability to that in the Hemiptera 
and Amphibia. In this case, however, the acrosome is so very 
small that it cannot be satisfactorily demonstrated until the time 
approaches for the casting off of the acroblast, when it can be 
made out as a small vesicle applied closely to the nuclear mem- 
brane (fig. 36). Then the acroblast separates from the acro- 
some proper (figs. 37 and 38), and passing rapidly back along 
the tail (fig. 39), remains visible as a conspicuous blackened ring 
for a considerable period. Its fate is doubtless similar to that 
in the Hemiptera. At the time the acroblast is cast off, the head 
of the sperm is usually bent rather sharply over, so that its major 
axis is nearly at right angles to that of the tail filament. It is 
accordingly difficult to say whether the acrosome is deposited 
directly in place and becomes subsequently anterior by the 
straightening out of the head; or whether there is an active migra- 
tion of the acrosome to its definitive position, as in the penta- 
tomids. Probably both factors play a part. At all events, the 
head eventually straightens out, and the acrosome can be made 
out as a minute body applied to its tip (fig. 40). Subsequently 
the head becomes much drawn out, as in other insect sperms. 
I have also been able to make some observations on the neben- 
kern which form an interesting supplement to my recent dis- 
cussion of this subject (Bowen, ’22b). In Lixus the nebenkern 
goes through a process of condensation quite similar to that 
