Page:Popular Science Monthly Volume 22.djvu/385

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371
SPECULATIVE ZOƖLOGY.

paleontological record is faulty through incompleteness, that of embryology is faulty through distortion and secondary modification. In general we do find the young stages of related species more like each other than the adults, and the distinctive characteristics of each are usually acquired gradually during the process of development; but this rule is by no means universal, and there are very many cases in

PSM V22 D385 Magnified views of an adult and growing sergestes.jpg
Fig. 6. Fig. 5.

which the adults of related species are more alike than the young, and in some cases the difference between the young forms is so great that their close relationship would hardly be suspected until each had been