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when naturalists are at work, they do not trouble themselves about the physiological value of the characters which they use in defining a
or in allocating any particular species. If they find a character nearly uniform, and common to a great number of forms, and not common to others, they use it as one of high value; if common to some lesser number, they use it as of subordinate value. This principle has been broadly confessed by some naturalists to be the true one; and by none more clearly than by that excellent botanist, Aug. St. Hilaire. If
characters are always found
→correlated with others,
though no apparent bond of
can be discovered between them, especial value is set on them. As in most groups of animals, important organs, such as those for propelling the blood, or for
it, or those for propagating the race, are found nearly uniform, they are considered as highly serviceable in classification; but in some groups
all these, the most important vital organs, are found to offer characters of quite subordinate value. Thus, as Fritz
has lately remarked, in the same group of crustaceans, Cypridina is furnished with a heart, whilst in
closely allied genera, namely Cypris and Cytherea, there is no such organ; one species of Cypridina has well-developed branchiæ, whilst another species is destitute of them. |
