The Embryology of Patella. 
5 
Sections of the ova at this period offen showed the presence 
of a layer of finely granulated protoplasm at the animal pole 
from which the pole globule arose. 
At times deep depressions would be formed in this region to 
the bottom of which the pole globales were attached. PL I, Fig. 5. 
After the extremities of tbe pole globule had fallen off, a 
small portion still remained attached to the ova, by means of 
which one was able to distinguish the animal pole as late as the 
stage with eight Segmentation spheres, 
Hl. Segmentation. 
Segmentation takes place according to the general Molluscan 
type and in its earlier stages very much resembles that of 
Planorbis as shown by Rabl. 
The first division is meridional, and in the majority of cases 
divides the ova into two uneqoal parts, PI. I, Fig. 9, although 
I have offen observed this stage when it was impossible to detect 
any difference in the two products. 
The next division is also meridional and at right angles to 
that of the first, only affecting however the larger of the two Seg¬ 
mentation spheres, which it divides into two equal parts. PI. I, 
Fig. 10. 
The division of the remaining first Segmentation sphere 
takes place some time af'terwards, but in the same plane as the 
second, giving rise to the stage with four Segmentation spheres. 
PI. I, Fig. 11. 
The third Segmentation, counting that of the two primary 
spheres as the second, although the division is not simultaneous, 
is parallel to the equator of the ova and a little nearer the 
animal than the vegetative pole. Instead however of dividing all 
four spheres simultaneously, it acts upon them successively, pro- 
ducing stages with five, six, seven and eight Segmentation spheres. 
PI. I, Fig. 12, 13 and 14. a ) 
The stage with six spheres is characteristic, having tliree 
small spheres superimposed upon three larger ones. I was not 
able to find the pole globule at this stage, therefore the ova can 
not be accurately oriented. 
1 ) I am inclined to think that an ineqnality of the two primary spheres is 
the normal condition, for although a difference in size between the first two spheres 
may not be discernible, a difference of some kind really exists since one invariably 
divides before the other. 
(153) 
