Variation in animals and plants (1902) (14801981783)

Identifier: variationinanima00vern (find matches)

Title: Variation in animals and plants

Year: 1902 (1900s)

Authors: Vernon, Horace Middleton, 1870-

Subjects: Variation (Biology)

Publisher: New York, H. Holt and company

Contributing Library: MBLWHOI Library

Digitizing Sponsor: MBLWHOI Library

Text Appearing Before Image:

ariation in certain mammals and winter birds ofEast Florida. Of a species of squirrel (Sciurus caroli-nensis), for instance, 2-8 individuals were measured,and these measurements are reproduced to scale in theaccompanying diagram. Here the animals are ar-ranged in order according to the length of their bodyin inches, and the corresponding values for the head,tail, and forefoot are given on the same ordinates. Bymeans of this diagram, the magnitude of each and allof the measurements made can be read off at a glance.The body was on an average 9.15 inches long, but theextreme values were 8.25 and 10.20 inches, or respect-ively 9.8 per cent, and 11.5 per cent, less and greaterthan the mean. The tail measurements were evenmore variable than this, the extremes varying from 6.75to 8.Y5 inches, or by respectively 14.3 per cent, and 11per cent, from the mean. In the forefoot the range ofvariation was less, and in the head smaller still; but* Bulletin Museum Comp. ZoOl,, Harvard, 1871. 10-5 10-0

Text Appearing After Image:

Body Tail Head Fore foot FIG. 1.—Variation of Sciurus carolinensis. 6 THE MEASUREMENT OF VARIATION. there was never any constancy, every animal varyingin respect of each of the measurements made. Thisis a point of fundamental importance, which cannot betoo thoroughly grasped. Every organism varies in re-spect of all its characters, whatever be their nature.The amount of this variation differs greatly, as theseresults well show, but it is always present in a greateror less degree. Another fact which this diagram bringsout very clearly is the comparative independence ofthese measurements. Because the body of one animalis longer than another, it by no means necessarily fol-lows that the head or tail is longer also. A superficialglance at this diagram might, indeed, lead one to sup-pose that the various parts of the body were absolutelyindependent of each other. But this we know not tobe the case. Between most parts and organs there is agreater or less degree of correlation, so that, on

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1902

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