The science of life : fully illustrated in tone and line and including many diagrams

th A ll A Ot SE Wr

THE EVIDENCE FROM PLANT AND ANIMAL STRUCTURE

that of quite other types of animals. To go human embryo ever has the “ gill-slits of a back to von Baer’s unlabelled specimens, fish.” But it has a transitory rude passage not only are the early embryos of man, through that type of structure. It is not,

cat, hen, and snake so alike that they are hard to tell apart, but one of the waysin which they are alike is in having their heart, main arteries, and neckregion built on the same plan as in

fish. Their heart is not divided,

wholly or partly, into right and left halves, but it is a single series of pumping chambers, just like the heart of a fish ; on the side of the neck is a series of clefts in just the position of a fish’s gillslits ; there is a series of arteries running down between the clefts just as infish ; and, indeed, the whole arrangement of blood = vessels and nerves and their relation to the clefts is piscine, and not in the least indicative of

Fig. 136. A collection of vertebrate embryos.

‘ I —le right, Man, Rabbit, Lizard, Each upright column represents the development of a single type—left to rig > Fe Newt, oe Dogfish the earliest embryos being below and the latest above. Note that the early stages

he or ie= Is are very like each other, and that the animals diverge as they develop. In ile ek Sees aia s olds are closing in to form the brain. Then the gill-clefts appear. In the ia oe preg ae in the newt and dogfish feathery gills appear. The human tail and its gr clearly seen.

: | ion ; it is an imperthe arrangement they themselves will show so to speak, a reproduction ; it 1s Pp later. These clefts never bear gills; the fect memory. . ad

: 7 -—indeed resemblance is not complete; the reader Once more this means poe aoe ce must not run away with the idea that the makes nonsense—if we are to

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