and the Evolution Hypothesis. 
517 
1877.] 
As yet, as far as I can discover, no evolutionist has 
pointed out the full significance of embryological phenomena 
in reference to the Evolution hypothesis. 
The analogy between the development of the individual 
and the unfolding of the primordial germ has been regarded 
hitherto only as a corroboration of the doCtrine of Descent. 
All organisms commence their existence, de novo , from 
the lowest types. Instead of at once developing the pa- 
rental characteristics they pass through metamorphoses 
similar to those which have, in past ages, succeeded each 
other in the progressive development of their families. 
This very striking parallelism of phenomena suggests , I think , 
the true solution of the mystery of Evolution. 
The faCt of the orderly reproduction of ancestral forms 
in the phases of individual development is so general that 
there can be no question as to its being a fundamental law 
of Nature. In order to illustrate its universality, I have 
chosen a few extracts from Dr. Carpenter’s “ Human Phy- 
siology,” and from the work of Oscar Schmidt already 
referred to. 
The first condition of the primordial germ is common to 
all animals, and is permanent in the lowest forms : there is 
no indication at this stage to what form of organic structure 
it may ultimately attain. Development commences by du- 
plicative subdivision ; a mass of cell-like bodies is thus 
produced whose component parts are all alike. This phase 
also has its parallel among the simpler organisms (the Hydra 
and Planaria). In all vertebrate animals the appearance of 
the primitive trace indicates the primary division to which 
they belong : this trace represents the vertebral column, and 
is first laid out as an unsegmented cord and an unsegmented 
sheath for the spinal cord ; this is the permanent state of 
the lower fishes. In the development of the Vertebrata the 
vitelline vessels correspond to the mesenteric veins of inver- 
tebrated animals, and the blastodermic vesicle is to be 
regarded as the temporary stomach of the embryo, remaining 
as the permanent stomach in the radiated tribes. The cir- 
culation of Mammalia is at first carried on exactly on the 
plan which is characteristic of the circulating apparatus of 
fishes. The aorta subdivides on either side of the neck into 
three or four arches, which are separated by fissures much 
resembling those forming the entrances to the gill-cavities 
of cartilaginous fishes ; and these arches re-unite to form 
the descending aorta, which transmits branches to all parts 
of the body. In the higher Vertebrata, however, the plan 
of the circulation is afterwards entirely changed by the 
