SHAPE OF THE NUCLEUS 6038 
nucleus in such elements. The peculiar shape of the head of 
the spermatozoon is doubtless an adaptation enabling it 
rapidly to move in fluids and to penetrate the ovum. In 
some instances, which have been described by Champy (4), 
the changes in the shape of the nucleus during the stages 
termed *Spermateleosis’ by Gatenby (7) are due to the 
influence of a special intranuclear apparatus. 
TEXT-FIG, 1]. 
A 
Fig. a.—Normal red blood corpuscle of bird with intranuclear 
rodlet faintly indicated. 
Figs. B and c.—Avian red cells after four days’ culture (pigeon’s red 
cells in chicken plasma), The nuclei have become swollen and the 
chromatin reduced in amount ; consequently the intranuclear 
rodlet is clearly visible. 
The latter is best studied in Amphibia such as Bom- 
binator, the Salamander, and the Axolotl. In these it 
can be seen within the spermatid as a thin and usually 
refringent rod, lying in the long axis of the nucleus. It appears 
to be developed from the centrosomes, originating from either 
the posterior or the anterior of these structures. Or sometimes 
it may be developed from both simultaneously. When the 
intranuclear rodlet does not extend the whole length of the 
nucleus, its free extremity, which may be bifid, is sometimes 
in relation with the nucleolus. All this is indicated in Pl. 24, 
fig. 1, which depicts spermatid nuclei from Bombinator. 
That this structure is not a fold in the nuclear membrane 
is seen in the figures of transverse sections of these nuclei, 
But it often co-exists with intranuclear canaliculi, from 
which, however, it can be further distinguished by its greater 
refringency. 
It is well known that the red blood corpuscles of birds have 
