« 
Embryology. 35 
precisely similar serics of events repeat themselves in 
each of these two cells, thus giving rise to four cells 
Fic. 39.—Segmentation of ovum. (After Tlickel.) Successive stages 
are marked by the letters A, B, C. D represents several stages in 
advance of C. 
(see Fig. 29). It must now be added that such’ 
duplication is continued time after time, as shown in 
the accompanying illustrations (Figs. 39, 40). 
All this, it will be noticed, is 
a case of cell-multiplication, 
which differs from that which 
takes place in the unicellular 
organisms only in its being zz- 
variably preceded (as far as we 
know) by karyokinesis, and in 
the resulting cells being all con- 
fined within a common envelope, Fic. 40.—The contents of 
: : an ovum in an advanced 
and so in not being free to daieho? ceeuenatlon, 
separate. Nevertheless, from drawn in perspective. 
what has already been said, it (After Hackel.) 
will also be noticed that this feature makes all the 
difference between a Metazoén and a Protozoén ; so 
that already the ovum presents the distinguishing 
character of a Metazoon. 
