434 FRANK R. LILLIE 
then, that the spermatozoén may be so injured in the process of 
centrifuging that it ruptures in the process of penetration, and we 
thus learn that partial sperm nuclei may come from spermatozoa 
merely injured and not actually broken in the process of centri- 
fuging. It should also be noted that in each of these cases the 
internal part of the spermatozoon is divided in two parts; presum- 
ably after penetration, by constriction around an injury. Fig. 
29 shows a condition similar in many respects to figs. 27 and 28, 
in that the entire spermatozo6n is present, and a large external 
part is separating from a smaller internal part. Figs. 30 and 31 
show the early penetration of parts of spermatozoa, recognizable 
as such merely by their small size'in the absence of the external 
part. The cases illustrated in figs. 80 and 31 are such as would 
be derived from injuries similar to those shown in figs. 20 and 21. 
Rotation of the sperm cone complex has already begun in figs. 
27 to 31, while the cone is much nearer the surface of the egg than 
in normal fertilization. Rotation begins immediately after pene- 
tration is completed, and hence takes place nearer to the surface 
when portions only of the sperm are concerned than when the 
whole sperm is concerned. In this connection the readershould 
compare figs. 9 and 10. 
' 
4. Stages of rotation of the partial sperm nuclei and origin of the 
sperm aster 
Convincing evidence of the partial nature of sperm nuclei in 
later stages of rotation and origin of the aster is difficult to secure, 
in spite of the fact that the control consisting of part of the same 
lot of eggs preserved immediately after centrifuging may show 
numerous instances of partial sperm heads like those illustrated 
in figs. 18 to 26. The difficulty of securing unequivocal evidence 
arises from the fact that mere size, except in extrerhe cases, is no 
longer a safe guide; in the first place the diameters of the nuclei 
vary only as the cube root of their volumes, hence considerable 
differences in volume may be represented by undetectable differ- 
ences of diameter. In the second place the sperm nuclei are not 
round and all are not in favorable positions for comparable meas- 
