Intermembral homologies : the correspondence of the anterior and posterior limbs of vertebrates / by Burt G. Wilder.

  • Burt Green Wilder
Date:
1871
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Licence: Public Domain Mark

Credit: Intermembral homologies : the correspondence of the anterior and posterior limbs of vertebrates / by Burt G. Wilder. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    now all the above examples are peripheral parts, and the like (ques- tions never would have arisen with such a part as a vertebra. Putnam [Am. Nat., Jan. 1872, j). 2G, note], mentions the slight tax- onomic value of air-bladder, head-scales, barbels, ventral fins and eyes, and Agassiz once figured fossil Crustaceans \_Eurypterun remipes and Pterygolus], as fishes on account of their external aspect. i Packard 2 has recognized the unreliability of characters drawn from peripheral and inconstant organs, like the mouth parts and wings; and Owen himself seems to recognize the principle, “Judge not according to appearances,” in the following paragraph : “ The prominent appearances which first catch the eye are deceptive; and the le.ss obtrusive phenomena which require searching out, more fre- (juently, when their full signification is reasoned upon, guide us to the right comprehension of the whole.” ® From the unpublished lectures on Selachians I again quote Agassiz: “ The Chimera; are generally separated from the other Selachians on account of a single branchial fissure ; but as this is a variable charac- ter, it should not set aside more internal characters.” A zoological illustration of our proposition is given in the great variety and disci’epancy of the definitions of the vertebrate type; so long as investigators regarded especially some one group with which they were more familiar, and so long as they included in their defi- nition of an abstract idea, the special structures which characterized those minor groups (see Agassiz, 201, 213), so long they-disagreed among themselves, and failed to follow Nature; this is seen in the difficulty which others have found in accepting Owen’s archet}q;e skeleton as correct; for it is essentially a piscine skeleton, and although the great anatomist holds that fishes depart least from the vertebrate archetype (63, 1, 102), such a generalization involves reasoning in a circle, and has been adopted by few (as Maclise, 23, 674-676). The Amphioxus is, without doubt, the simplest known vertebrate; but it cannot be regarded as the material manifestation of the verte- brate idea, since its structure presents positive characters by which ^ Microscopic section of the tooth of Ceratodus has convinced Mr. Bicknoll tlint it is “ unsafe to found genera or even species upon the microscopical structure of a single tooth or bone, although it has proved correct in many cases.” Proc. Host. Soc. Nat. Hist., April 19th, 1871. ’ Guide to the Study of Insects, p. 14. ’ Pala:ontology, p. 367,