18 
SPERMATOGENESIS OE NORMAE 
Sphere takes stain more intensely and appears more dense as 
soon as the above change has occurred and there are visible 
frequently minute star-like radiations of a lighter staining sub¬ 
stance which spring out from the clear area around the centro- 
some (Fig. 7, i.). The radiations remind one of the clear-look¬ 
ing streaks which accompany the formation of the pulsating 
vaculole in some of the infusoria. 
What the interpretation of the above facts is, can be an¬ 
swered at present only conjecturally. The first thought that 
presented itself was that the centrosome originally lay inside 
the nucleus and that the above occurrence was a process of ex¬ 
trusion by which it reached the sphere. But careful examina¬ 
tion of the cells reveals the presence of the centrosome in the 
sphere long before synapsis. Indeed it seems to originate from 
the sphere substance itself and to increase in size as the sphere 
develops. 
It is possible that the passage of substance from the nucleus 
to the sphere may have something to do with the formation of 
the spindle, for immediately after synapsis the centrosome 
divides and the spindle fibres appear. It may be that some 
substance is required from the nucleus before the extremely 
heavy spindle of this division period can be constructed. 
The sphere in the germinal cells of the pigeon seems to be 
simply a very plastic area of the cytoplasm especially favorable 
for building up into such structure as spindles, asters, centro- 
somes, the apex of the head, and the axial fibre of the sperma¬ 
tozoon tail. That such a role on the part of the sphere is of very 
general occurrence in germ cells is so well known to workers in 
spermatogenesis as not to require specific reference. In the 
ovarian egg the sphere (idiozome) seems to be employed like¬ 
wise in diverse, ways. In one case of abnormal ovarian struc¬ 
ture in the pigeon (Guyer^) where numerous multiple eggs were 
forming and extensive degeneration going on, the sphere 
seemed actively employed in building up cell membranes as 
well as in the formation of fibres. The large, vacuoles which 
were present in many eggs, moreover, originated invariably in 
1. Guyep, M. P: Ovarian Structure in an Abnormal Pigeon.-—Zool. Bull II, 
No. 5, 1899. 
