nidae
(genera _Pycnogonum_ and _Phoxichilus_).

_Remarks._--The Pantopoda are not known in the fossil condition. They
are entirely marine, and are not uncommon in the coralline zone of the
sea-coast. The species are few, not more than fifty (23). Some large
species of peculiar genera are taken at great depths. Their movements
are extremely sluggish. They are especially remarkable for the small
size of the body and the extension of viscera into the legs. Their
structure is eminently that of degenerate forms. Many frequent growths
of coralline Algae and hydroid polyps, upon the juices of which they
feed, and in some cases a species of gall is produced in hydroids by
the penetration of the larval Pantopod into the tissues of the polyp.

Sub-Class II. (of the Nomomeristic Arachnida). EU-ARACHNIDA.--These
start from highly developed and specialized aquatic branchiferous
forms, exhibiting a prosoma with six pediform pairs of appendages, an
intermediate prae-genital somite, a mesosoma of six somites bearing
lamelliform pairs of appendages, and a metasoma of six somites devoid
of appendages, and the last provided with a post-anal spine. Median
eyes are present, which are monomeniscous, with distinct retinal and
corneagenous cell-layers, and placed centrally on the prosoma. Lateral
eyes also may be present, arranged in lateral groups, and having a
single or double cell-layer beneath the lens. The first pair of limbs
is often chelate or prehensile, rarely antenniform; whilst the second,
third and fourth may also be chelate, or may be simple palps or
walking legs.

An internal skeletal plate, the so-called "entosternite" of
fibro-cartilaginous tissue, to which many muscles are attached, is
placed between the nerve-cords and the alimentary tract in the prosoma
of the larger forms (_Limulus_, _Scorpio_, _Mygale_). In the same and
other leading forms a pair of much-coiled glandular tubes, the coxal
glands (coelomocoels in origin), is found with a duct opening on the
coxa of the fifth pair of appendages of the prosoma. The vascular
system is highly developed (in the non-degenerate forms); large
arterial branches closely accompany or envelop the chief nerves;
capillaries are well developed. The blood-corpuscles are large
amoebiform cells, and the blood-plasma is coloured blue by
haemocyanin.

The alimentary canal is uncoiled and cylindrical, and gives rise