arvae, than do the females; whereas amongst insects, as in
the case of the glow-worm in Coleoptera, and of certain nocturnal
Lepidoptera, it is the female which retains an embryonic
character, being worm-like or caterpillar-like, without wings.
But in all these cases, the male is more locomotive than the
female.

If we look for analogies to the facts here given, we shall find them in
the Lerneidae already alluded to, but in these the males are not
permanently attached to the females, only cling, I believe, to them
voluntarily. The extraordinary case of the Hectocotyle, originally
described as a worm parasitic on certain Cephalopoda, but now shown by
Koelliker to be the male of the species to which it is attached, is
perhaps more strictly parallel. So again in the entozoic worm, the
_Heteroura androphora_ the sexes cohere, but are essentially distinct:
"this singular species, however," according to Professor Owen,[49]
"offers the transitional grade to that still more extraordinary
Entozoon, the _Syngamus trachealis_, in which the male is organically
blended by its caudal extremity with the female, immediately anterior to
the slit-shaped aperture of the vulva. By this union a kind of
hermaphroditism is produced; but the male apparatus is furnished with
its own peculiar nutrient system; and an individual animal is
constituted distinct in every respect, save in its terminal confluence
with the body of the female. This condition of animal life, which was
conceived by Hunter as within the circle of physiological possibilities,
has hitherto been exemplified only in the single species of Entozoon,
the discovery of the true nature of which, is due to the sagacity and
patient research of Dr. C. Th. Von Siebold." In Ibla, the males and
females are not organically united, but only permanently and immovably
attached to each other. We have in this genus the additional singularity
of occasionally two males parasitic on one female.

[49] Cyclopaedia of Anatomy and Physiology, p. 142.

I have used the term parasitic, which perhaps ought strictly to be
confined to cases where one creature derives its nutriment from another,
inasmuch as the male is invariably and permanently attached to and
imbedded in the female,--from its being protected by her capitulum, so
that its own capitulum is not developed--and from its feeding on minute
animals infesting her sack. The male Ibla must seize its prey, guided
probably by its we