CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 
633 
The specific gravity of the spermatozoon 
The sperm head is sometimes spoken of as the condensed nu- 
cleus of the spermatid. If by condensation is meant a more sohd, 
i.e., less watery consistence the centrifuge would give evidence of 
the fact, for by its means bodies having differences in weight are 
sorted out. The evidence shows that the sperm head remains 
in that part of the egg where it enters and therefore is not either 
heavier or lighter than the general cytoplasm. The failure to move 
the chromosomes of the egg points in the same direction, but their 
attachment to the spindle might prevent their movement unless 
their weight were sufficient to drag the asters with them. Yet 
even at the dissolution of the nucleus, and before the fibre system 
is fully developed, the chromosomes can not be moved in any of the 
eggs that I have studied. As soon as the sperm head begins to 
become vacuolated its transportation in the cytoplasm is made 
possible. This is due beyond doubt to the material contained in 
the vacuoles being lighter than the c}- toplasm. The watery nature 
of some of this material is therefore probable. 
The head of the sperm contains in addition to the original 
cell-nucleus the condensed cytoplasm of the spermatid. An 
examination of the formation of the spermatozoon shows that the 
cytoplasm shrinks around the elongated nucleus, but there is no 
evidence that any of the cytoplasm is lost. Its diminution would 
seem to be due to loss of watery fluid, and if the presence of a 
more watery fluid in the nuclei makes them lighter its loss in the 
cytoplasm would increase the weight of the latter. If then the sur- 
rounding pellicle of the protoplasm of the sperm is denser than 
ordinary cytoplasm this element should increase the chance of the 
sperm centrifuging to the heavier pole. But, as stated, there is no 
evidence of such transportation. 
On the other hand the comparison includes cells from differ- 
ent organs of different individuals, and even if the sperm is denser 
than the spermatid it need not follow that it is therefore denser 
than the egg. The evidence shows however that if there is any dif- 
ference it is not shown by a centrifugal force sufficient to separate 
other constituents of the egg no larger than the sperm head. 
