Embryology. 119 
find. Take, for example, the case of the highest 
organism, Man. Like that of all other organisms, 
unicellular or multicellular, his development starts 
from the nucleus of a single cell. Again, like that 
of all the Metazoa and Metaphyta, his development 
starts from the specially elaborated nucleus of an 
egg-cell, or a nucleus which has been formed by 
the fusion of a male with a female element?. When 
his animality becomes established, he exhibits the 
fundamental anatomical qualities which characterize 
such lowly animals as polyps and jelly-fish. And 
even when he is marked off as a Vertebrate, it cannot 
be said whether he is to be a fish, a reptile, a bird, 
or a beast. Later on it becomes evident that he is 
to be a Mammal; but not till later still can it be said 
to which order of mammals he belongs. 
Here, however, we must guard against an error which 
is frequently met with in popular expositions of this 
psubject. It is not true that the embryonic phases 
in the development of a higher form always resemble 
\so many adult stages of lower forms. This may or 
eee not be the case; but what always is the case 
1 Tt has already been stated that both parthenogenesis and gemmation 
are ultimately derived fiom sexual reproduction. It may now be added, 
on the other hand, that the earlier stages of parthenogenesis have been 
observed to occur sporadically in all sub-kingdoms of the Metazoa, 
including the Vertebrata, and even the highest class, Mammalia. These 
earlier stages consist in spotaneous segmentations of the ovum; so 
that even if a virgin has ever conceived and borne a son, and even if 
such a fact in the human species has been unique, still it would not be- 
token any breach of physiological continuity. Indeed, according to 
Weismann’s not improbable hypothesis touching the physiological 
meaning of polar bodies, such a fact need betoken nothing more than 
a slight disturbance of the complex machinery of ovulation, on account 
of which the ovum failed to eliminate from its substance an almost 
inconceivably minute portion of its nucleus. 
