Variation in animals and plants

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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

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ir degree of devia-tion from it, so that finally, beyond the extreme devia-tions of 9.6 and 11.7 inches, no measurements were ob-served at all. The number of observations here plotted out is ob-viously much too small to yield at all a regularseries, but it is quite sufficient to show that the 9-5 10-0 10-5 11-0 H-5 FIG. 2.—Wing of Sterna Mrundo. measurements are by no means evenly distributedthrough the whole range of their variation. There isa most conspicuous collection of them, or heaping up,in the region of the mean measurement. Supposingthe number of observations were increased, thenone would expect as a general rule to get a more andmore even series; in fact, to get a fairly accurate ideaas to the kind of series obtainable, supposing an in-finite number of observations were made. In Fig. 3is plotted out a curve representing the distribution of1923 measurements made by Warren * on a certaindimension, viz., the carapace breadth of the crab Por- *Proc. Roy. Soc., vol. Ix. p. 225.
Text Appearing After Image:
10 THE MEASUREMENT OF VARIATION. tunus depurator. In order to get rid as far as possibleof the factor of size, and obtain a measure of the varia-bility apart from this, each measurement was calculatedas a fraction on that of the carapace length of thecrab taken as 1000. The numbers on the abscissa linetherefore represent 1230, 1240, etc., thousandths ofthe total length. The figures on the central ordinaterepresent the numbers of individuals of each particulardimension. For instance, one may gather that 16 indi-viduals had a post-spinous length of 1260,172 of themone of 1297, and so on. If this curve be compared with the general contourof the previous figure, it will be seen at a glance thatthere is a much more regular rise and fall, especially inregard to the extreme measurements. In fact, it doesnot differ very greatly from the dotted line curve uponwhich it is superposed, and supposing the number ofobservations had been greater, one would expect theapproximation to be still closer;

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