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Books > Science & Mathematics > Science: general issues > History of science
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Facts and Arguments for Darwin - With Additions by the Author (Paperback)
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Facts and Arguments for Darwin - With Additions by the Author (Paperback)
Series: Cambridge Library Collection - Darwin, Evolution and Genetics
Expected to ship within 12 - 19 working days
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Excerpt: ...is presented by the Hyperinae which usually live upon
Acalephae. In these the young and adults often have a remarkably
different appearance; but even in these there is no new formation
of body-segments and limbs, but only a gradual transformation of
these parts. ( In the young of Hyperia galba Spence Bate did not
find any of the abdominal feet, or the last two pairs of thoracic
feet, but this very remarkable statement required confirmation the
more because he examined these minute animals only in the dried
state. Subsequently I had the wished-for opportunity of tracing the
development of a Hyperia which is not uncommon upon Ctenophora,
especially Beroe gilva, Eschsch. The youngest larva from the
brood-pouch of the mother already possess THE WHOLE of the thoracic
feet; on the other hand, like Spence Bate, I cannot find those of
the abdomen. At first simple enough, all these feet soon become
converted, like the anterior feet, into richly denticulated
prehensile feet, and indeed of three different forms, the anterior
feet (Figure 44) the two following pairs (Figure 45) and finally
the three last pairs (Figure 46) being similarly constructed and
different from the rest. In this form the feet remain for a very
long time, whilst the abdominal appendages grow into powerful
natatory organs, and the eyes, which at first seemed to me to be
wanting, into large hemispheres. In the transition to the form of
the adult animal the last three pairs of feet (Figure 49)
especially undergo a considerable change. The difference between
the two sexes is considerable; the females are distinguished by a
very broad thorax, and the males (Lestrigonus) by very long
antennae, of which the anterior bear an unusual abundance of
olfactory filaments. Their youngest larvae of course cannot swim;
they are helpless little animals which firmly cling especially to
the swimming laminae of their host; the adult Hyperiae, which are
not unfrequently met with free in the sea, are, as is...
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