288 CONCLUDING REMARKS (Cuar. XV. 
genera are provided with such small roots,* and that Aldro- 
vanda is quite rootless; about the roots of the two other 
genera nothing is known. It is, no doubt, a surprising fact 
that a whole group of plants (and, as we shall presently see, 
some other plants not allied to the Droseracee) should 
subsist partly by digesting animal matter, and partly by 
decomposing carbonic acid, instead of exclusively by this 
latter means, together with the absorption of matter from 
the soil by the aid of roots. We have, however, an equally 
anomalous case in the animal kingdom ; the rhizocephalous 
crustaceans do not feed like other animals by their mouths, 
for they are destitute of an alimentary canal; but they live 
by absorbing through root-like processes the juices of the 
animals on which they are parasitic.t 
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,t which range in the Old World from the Arctic 
regions to Southern India, to the Cape of Good Hope, 
* [Fraustadt (Dissertation, Breslau, 
1876) shows that the roots of Dionza 
are by no means small. In another 
Breslau Dissertation (1887) Otto 
Penzig shows that the roots of 
Drosophyllum lusitanicum are also 
well developed. Pfeffer (‘ Landwirth. 
Jahrbucher,’ 1877) points out that the 
argument from the small develop- 
ment of roots in some carnivorous 
plants is valueless, because the same 
state of things is found in many 
marsh and aquatic plants which 
neither catch nor digest insects.— 
F. D.] 
+ Fritz Miiller, ‘Facts for Darwin,’ 
Eng. trans. 1869, p. 1389. The rhizo- 
-cephalous crustaceans are allied to 
the cirripedes. It is hardly possible 
to imagine a greater difference than 
that between an animal with pre- 
hensile limbs, a well-constructed 
mouth and alimentary canal, and one 
destitute of all these organs and 
feeding by absorption through branch- 
‘ing 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 Miiller 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 Lepadide, ‘Ray Soc.’ 1851, 
p. 169) are in a most feeble and 
almost rudimentary condition. Dr. 
R. Kossmann has given a very in- 
teresting discussion on this subject 
in his ‘Suctoria and Lepadide,’ 1873. 
See also, Dr. Dohrn, ‘Der Ursprung 
der Wirbelthiere,’ 1875, p. 77. 
{~ Bentham and Hooker, ‘Genera 
Plantarum.’ Australia is the me- 
tropolis of the genus, forty-one 
species having been described from 
this country, as Prof. Oliver informs 
me. 
