40 ADAM SEDGWICK. 
is the mode of formation of the head and trunk in these 
animals.” 
This, I think, shows quite clearly Darwin’s view of the 
matter, 
Huxley, in his ‘Man’s Place in Nature,’ says :—“ The his- 
tory of the development of any other Vertebrate animal—lizard, 
snake, frog, or fish—tells the same story. There is always, to 
begin with, an egg having the same essential structure as that 
of the dog; the yolk of that egg undergoes division or seg- 
mentation, as it is called, the ultimate products of that seg- 
mentation constitute the building materials for the body of the 
young animal; and this is built up round a primitive groove, 
in the floor of which a notochord is developed. Furthermore, 
there is a period in which the young of all these animals 
resemble one another, not merely in outward form, but in all 
essentials of structure, so closely, that the differences between 
them are inconsiderable, while in their subsequent course they 
diverge more and more widely from one another.” 
Tue SIGNIFICANCE OF ANCESTRAL RUDIMENTS IN 
Emsryonic DEVELOPMENT. 
The existence of a phase at the beginning of life during 
which a young animal acquires its equipment by a process of . 
growth of the germ, is of course intelligible enough. We see 
such a phase in the formation of buds, and in the sexual repro- 
duction of both animals and plants. The remarkable point is 
that while in most cases this embryonic growth is a direct and 
simple process—e.g. animal and plant buds, embryonic de- 
velopment of plant seeds—in some cases—e.g. most cases of 
sexual reproduction of animals—it is a circuitous one, and the 
embryonic phase shows stages of structure which seem to 
possess a meaning other than that of being merely phases of 
growth. 
As is well known, the explanation which is given of this 
circuitous course of embryonic development is that we are 
dealing with a special case of the law of heredity— each 
