6 
The Embryology of Patella. 
The stage with seven spheres I have not with certainty 
been able to find, but think that such a stage exists. 
The stage with eight spheres is represented in PI. I, Fig. 14. 
It will be seen that there is a slight difference in size between 
the four cells of the two poles of the egg, while otherwise, so 
far as could be observed, they were of the same color and structure. 
By a further division of the cells the ova become transformed 
into a blastosphere with a slightly eccentric and oval Segmen¬ 
tation cavity. 1 ) 
In surface views of the vegetative pole of such an embryo, 
may be observed four large cells, only distinguished from the 
remaining ones by their coarser structure; in optical section 
it will be seen that the gradation in size of these four cells to- 
ward the smaller ones at the opposite pole is very gradual. Sub- 
sequent development shows that tbose four cells constitute the 
beginning of the endoderm. 
Yery early in the Segmentation stages the thick chorion falls 
away from the embryo leaving it free to undergo further deve¬ 
lopment. It is seldom that I have observed embryos at the end 
of the Segmentation still enclosed within the chorion, — never af'ter 
that period. 
IV. Gastrulation. 
It is difficult to determine the characters by which one can 
decide when the gastrulation begins since there is no invagination 
of the endoderm to determine t-his point. We will consider the 
beginning of the gastrulation, and henee the second period of 
development, as being indicated by the division of the four primi¬ 
tive endoderm cells and their growth inwards to fill up the Seg¬ 
mentation cavity. It is also at this period, or possibly a little 
before, that the rudiments of the velum and apical plate appear. 
At the end of the preceding period four long cells. with 
difficulty to be distinguished from the surrounding ones, were to 
q It must be remarked here that owing to tbe great opacity of tbe ova, 
the uniformity in size of the Segmentation spheres and their indistinct bound- 
aries, and owing to the artifical condition, which produced' a large percentage of 
abnormal types, in the earlier stages difficult to distinguish from the normal ones, — 
it was difficult. to follow with certainty the rbythm in the Segmentation after the 
eight — cell stage. Hence the succeeding stages as far astbe blastosphere have been 
omitted, since I am unable to say with certainty whether the results were those 
of a normal development or not. 
(154) 
