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CHAPTER IV.
BROOKS’s Law.
With a general description of the post-embryonal development of a few
species of Cypridiniformes and Halocypriformes.
Among the material of the Stomatopods that was collected during the
Challenger expedition, 1873—1876, there was also a very rieh collection of pelagian
larvae. This caused W. K. BROOKS, who examined this material, to make an attempt to
„unravel the tangled thread of the larval history“ of this group, one of the most difficult
problems that are presented in the study of post-embryonal development in the Crustacean
group. W. K. BROOKS presented the result of these studies of his in a large work, „R e p o r t
on the Stomatopoda, etc.“, 1886.
In attempting to identify the different larval stages this author made use of (1) the
greater or less resemblance of the different individuals and (2) comparative measurements.
The method of comparative measurements seems to have given very good results, as
is shown by the following statement on p. 5: ,,the measurements usually enabled me to decide
with confidence whether a given larva does or does not belong to a certain series.“ From a
general point of view the greatest interest of the investigation is perhaps centred in this point.
This method gave the best results in the study of four larvae that were caught
at the same time off Cape St. Vincent. This author writes as follows about this, p. 5:
,,In a few cases these comparative measurements gave proofs of specific identity which
could hardly be made more conclusive by rearing the larvae. Thus the lengths of the series of
Coronis larvae shown in pi. XIII, figs. 1—8 are as follows, and if the length of the first stage
be successively multiplied by five-fourths of itself, and this number by five-fourths of itself
again, and so on, weobtain the series of numbers given in the second line, and as it is not
conceiv-able that an accidentai collection of larvae should exhibit such exact conformity to a numerical
law, we may feel certain that these larvae, are genetically related, that they belong to one
species or else to closely related species, and that the series is consecutive, with the exception
of one missing stage before the last.
/ nlroductoru
notes.
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