432 FRANK R. LILLIE 
head of the spermatozo6n is present as shown by the middle 
piece, but it has been drawn out to a band and shows its granu- 
lar structure. Fig. 19 shows a case in which the middle piece 
and a small part of the base of the sperm head has been entirely 
removed. Figs. 20, 21, 22 and 23 show the removal of increas- 
ingly large portions of the sperm head. Cases could be illus- 
trated beyond either end of this series in which on the one hand 
the spermatozo6n is entirely uninjured, and on the other hand 
even the perforatorium is pulled out of the entrance cone. The 
eases illustrated are merely selections from a very much larger 
set of observations. 
It is shown, therefore, that practically any degree of injury to 
the spermatozo6n may be produced prior to its entrance. Cases 
in which the delicate perforatorium is broken next the head leav- 
ing only the cone and attachment granules are the most common 
as is to be expected; but the other classes of injury bear witness to 
the tenacity of the hold of the spermatozo6n on the egg. 
b. Injuries to the spermatozoén after penetration has begun. 
This class of injuries is relatively rare because the actual process 
of penetration requires only about two minutes, and the chances 
of involving it are therefore correspondingly few. However, I 
have found a considerable number of such cases in the prepara- 
tions. At first I looked to such injuries as the only source of the 
partial sperm nuclei already observed in the egg, but as made the 
observations described in the preceding section, I realized that 
they were not the only or indeed the chief source of such partial 
sperm nuclei. Figs 24 and 25 illustrate two cases from the same 
experiment (6.5.1, 1911) from which figs. 18 to 23 are taken. In 
fig. 24 it will be seen that penetration has already begun (cf. fig. 6), 
and the external part of the spermatozo6n is ravelled out and the 
middle piece, at least, lost. Fig. 25 is a little more complicated; 
in this case penetration had probably reached a condition inter- 
mediate between figs.6and7. The centrifugal force has doubled 
up the part of the sperm in the egg, and drawn out the external 
part removing the middle piece. Fig. 26, finally, is a clear cut 
case, the external part alone being removed entirely, and the 
remainder showing a clear penetration picture. This is the prob- 
