File:Evolution and its relation to religious thought (1888) (14577376997).jpg

Identifier: evolutionitsrela00leco (find matches)
Title: Evolution and its relation to religious thought
Year: 1888 (1880s)
Authors: LeConte, Joseph, 1823-1901
Subjects: Evolution Religion and science
Publisher: New York, D. Appleton
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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f a fish; b, one arch with fringe (after Owen); H, the heart. course, necessary, for they are the gill-arclies. Thewhole of the blood passes through these arches, to beaerated in the gill-fringes. The use of this peculiarstructure is here obvious enough. If a lizard were eyera fish, and afterward turned into a lizard, changing itsgill-respiration for lung-respiration, then, of course, theuseless gill-arches would remain to tell the story. Now,although a lizard never was a fish, in its individual his-tory or ontogeny, it was a fish in its family history orphylogeny, and therefore it yet retains, by heredity, thiscurious and useless structure as evidence of its ancestry. That this is the true explanation is demonstrated bythe fact that in amphibians this very change actually 13G EVIDENCES OF THE TRUTH OF EVOLUTION. takes place before our eyes in the individual history. Wehave already seen that the individual frog, in its tadpolestate, is a gill-breather. It has therefore its gill-arches
Text Appearing After Image:
Fig. 39. Figs. 38, 39,—Diagrams showing tlie change of the course of blood inthe development of a frog. 38. The tadpole stage. 39. The maturecondition, h, heart; ggg, external gills ; y^^, internal gills;c c, connecting branches in the tadpole; pp, pulmonary branches. PKOOFS FPwOM EMBRYOLOGY. I37 (Fig. 38), three on each side, like a fish, and for the samereason, yiz., the aeration of the blood. But when its gillsdry up and lung-respiration is established, its now uselessgill-arches still remain as aortic arches, to attest theirprevious condition (Fig. 39). Now, the lizard undoubt-edly came from an air-breathing, tailed ampliibian, andtherefore inherited this form of arterial distribution. Inboth lizard and amphibian the ultimate cause is an originfrom fishes, in which such arches are obyiously necessary.The diagrams. Figs. 38 and 39, are illustrations some-what idealized, showing the manner in which the changeactually takes place in air-breathing amphibians. Fig.38 represents the t

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