Of the six genera, Drosera has been incomparably the most successful in
the battle for life; and a large part of its success may be attributed
to its manner of catching insects. It is a dominant form, for it is
believed to include about 100 species,** which range in the Old World
from the Arctic regions to Southern India, to the Cape of Good Hope,
Madagascar, and Australia; and in the New World from Canada to Tierra
del Fuego. In this respect it presents a marked contrast with the five
other genera, which appear to be failing groups. Dionaea includes only
a single species, which is confined to one district in Carolina. The
three varieties or closely allied species of Aldrovanda, like so many
water-plants, have a wide range from Central Europe to Bengal and
Australia. Drosophyllum includes only one species, limited to Portugal
and Morocco. Roridula and Byblis each have (as I
* Fritz Muller, Facts for Darwin, Eng. trans. 1869, p. 139. The
rhizocephalous crustaceans are allied to the cirripedes. It is hardly
possible to imagine a greater difference than that between an animal
with prehensile limbs, a well-constructed mouth and alimentary canal,
and one destitute of all these organs and feeding by absorption through
branching root-like processes. If one rare cirripede, the Anelasma
squalicola, had become extinct, it would have been very difficult to
conjecture how so enormous a change could have been gradually effected.
But, as Fritz Muller remarks, we have in Anelasma an animal in an
almost exactly intermediate condition, for it has root-like processes
embedded in the skin of the shark on which it is parasitic, and its
prehensile cirri and mouth (as described in my monograph on the
Lepadidae, Ray Soc. 1851, p. 169) are in a most feeble and almost
rudimentary condition. Dr. R. Kossmann has given a very interesting
discussion on this subject in his Suctoria and Lepadidae, 1873. See
also, Dr. Dohrn, Der Ursprung der Wirbelthiere, 1875, p. 77.
** Bentham and Hooker, Genera Plantarum. Australia is the metropolis
of the genus, forty-one species having been described from this
country, as Prof. Oliver informs me. [page 358]
hear from Prof. Oliver) two species; the former confined to the western
parts of the Cape of Good Hope, and the latter to Australia. It is a
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