260 
0. F. U. MEEK. 
Conclusion. 
Id tlie introduction of this paper I have said that the 
measurements to be made in the course of these investigations 
may suggest a further generalisation in the problem of 
mitosis. We have now made these measurements, and have 
found that they do suggest a new generalisation, viz. that 
the length of the mitotic spindle at the conclusion of the 
metaphase is proportional to the radins of a sphere eqnal in 
volume to the cell. 
The measurements upon which this proposition is based 
have been made with great care ; bnt it is possible that 
coincidence is responsible for the connection found between 
the spindle length and cell volume in the spermatocytes, 
and for the apparent connection in the spermatogonia. If, 
however, coincidence is not responsible, correlation is estab- 
lished between these phenomena in the spermatogenetic 
metaphases of this species. I intend in subsequent papers to 
measure spindle lengths at corresponding stages in other 
organisms; and, if the same relationships are found, I hope 
that my results will be corroborated by those of other 
cytologists. 
Summary. 
(1) The length of the mitotic spindle, i.e. the distance 
between the two centrosomes, at the stage of the metaphase 
when the chromosomes are undergoing constriction in the 
equatorial plane, appears to be a constant for each spermato- 
genetic mitosis of the species. The lengths found are 6'9, 
10*2 and 7'8 fn for the secondary spermatogonia aud primary 
and secondary spermatocytes respectively. 
(2) The length of the mitotic spindle at the conclusion of 
the metaphase when the daughter-chromosomes are ready to 
move apart appears to be a constant for each spermatogenetic 
mitosis of the species. The lengths found are 7' I, 10'4 and 
8T ju for the secondary spermatogonia aud primary and 
secondary spermatocytes respectively. 
(3) The length of the mitotic spindle in the earliest 
