Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

386 A R A C H N I D E S.
Arach- sometimes excepted. Two mandibles (antenne-pinces or
nides. cheliceres of Latreille) terminated by a couple of fingers;
and two maxillae formed by the first article of the palpi.
This family consists of two genera, the habits of which
are terrestrial; their bodies oval or oblong.
Genus Galeodes, Oliv. Solpuga, Lichtenstein.
Mandibles very large, with vertical, strongly toothed
fingers, of which one is superior, fixed, frequently fur¬
nished at its base with a slender pointed appendage; the
other movable. Palpi large, advanced, in the form of
feet or of antennas, terminated by a short button-shaped
article, vesicular and hookless. Anterior pair of feet re¬
sembling the palpi, but smaller; they are also hookless.
Each of the other feet has the terminal joint of the tarsus
furnished with a pair of hooks. The posterior pair of feet
have five remarkable scaly excrescences placed upon
foot-stalks, and ranged along the inferior surface of their
first two articulations. The eyes, two in number, are very
close to each other, and are situated on an eminence of
the anterior portion of the first segment of the thorax,
which presents the appearance of a large head bearing
the anterior pair of feet, in addition to the masticating
organs.
According to M. Dufour the terminal article of the
palpi incloses a particular disc-shaped organ, of a whitish
colour and pearly lustre, not visible externally unless the
animal is irritated. The lip (labre) has the form of a small
beak, much compressed, recurved, pointed, and hairy.
The languette is small, keel-shaped, and terminates in two
divergent threads, each placed on a small articulation.
Latreille perceived a pretty large stigmatic opening on
each side of the body, between the first and second feet,
and another cleft at the base of the abdomen. The ab¬
domen is oval and composed of nine rings. We lately re¬
ceived two species of this genus from Persia.
Sp. Araneoides, Olivier. (PI. XLVII. fig. 1.)—Solpuga
Arachnoides, Herbst.—Colour pale yellowish-brown. In¬
habits Africa and the western countries of Asia.
Genus Chelifer, Geoff. Obisium, Uliger. — Palpi
elongated, furnished with didactile pincers at their
extremity. Eyes placed on the sides of the thorax.
Legs nearly equal in size, each terminated by a pair of
crotchets. Body flat. Thorax almost square.
These animals run swiftly, both backwards and for¬
wards. They carry their eggs about with them after the
manner of spiders. The elder Hermann is of opinion
that they spin webs. Such of the species as have the tho¬
rax divided or impressed by a transverse line form the
genus Chelifer of Dr Leach. Their eyes are two in num¬
ber. Others have the thorax undivided, and of these
the eyes amount to four. They form the genus Obisium
of the last-named author.
&p. Fasciatus.—Hands oval. Segments of the abdo¬
men bordered with white. Lives beneath the bark of
willow and other trees. Sometimes occurs near London.
Leach, in Linn. Trans, xi.
Sp. Cancroides. (PI. XLVII. fig. 2.)—This species mea¬
sures about a line and a half in length. The body and
legs are of a reddish brown. The palpi are about twice
the length of the body. It is a European species, inha¬
biting old books, herbariums^ &c. and preys upon the
bodies of several destructive insects. It ought therefore
to be cherished in the live state by collectors.
Family II.—Pycnogonides. Arach.
Trunk composed of four segments, occupying almost
the entire length of the body, terminated at each extre¬
mity by a tubular article, of which the anterior portion,
sometimes simple, sometimes accompanied by mandibles
(antenne-pinces) and palpi, or by one or other of these or¬
gans, constitutes the mouth. Both sexes have eight feet
proper for running ; but the females are moreover provid¬
ed with two false feet, placed near the anterior pair, and
serving to carry the eggs.
The species of which this family is composed inhabit
the sea. They usually keep themselves concealed among
sea-weed along the shores, and feed upon small marine
animals. Their movements are slow. Their bodies are
generally linear, the legs very long, composed of from
eight to nine articles, and terminated by two unequal crot¬
chets, of which the smaller is cleft. The first articula¬
tion of the body, or that which represents the head and
mouth, forms an advanced, nearly cylindrical tube, pierc¬
ed at its extremity by a triangular opening. It also bears
the mandibles and palpi. The former are linear or cylin¬
drical, composed of two pieces, of which the last is pin-
cer-shaped, with the inferior or fixed claw shorter than the
other. The palpi are filiform, with a crotchet at the end,
and composed of from five to nine articles. Each of the
succeeding segments of the body, with the exception of
the last, serves as a point of attachment to a pair of legs;
and the segment which articulates with the mouth is pro¬
vided on its dorsal portion with a tubercle bearing the
eyes, and on its ventral portion (in the females) with a
small additional pair of feet on which the eggs are distri¬
buted. The terminal segment is small, cylindrical, and
pierced at its extremity. The stigmatic openings in the
bodies of this family have not yet been discovered.1
M. Savigny is of opinion that this family forms the na¬
tural transition from the class Arachnides to the crustace-
ous tribes, and great uncertainty still prevails in the minds
of naturalists regarding their true position in the system.
We place them in the position which they now occupy in
our present arrangement, in accordance with the views of
M. Latreille. M. Milne Edwards, who has studied these
animals in their native places, informed that celebrated
entomologist, that in the interior of the Pycnogonides
he observed caeca or lateral expansions of the intestinal
canal.
Genus Pycnogonum, Brunnich.—In this genus the man¬
dibles and palpi are wanting, and the length of the feet
scarcely exceeds that of the body, which is proportion¬
ally short and thick. The species are parasitical on
cetaceous animals.
Sp. Balcenarum. (PI. XLVII. fig. 3.)—Phalangium
Balcenarum, Linn.—Inhabits the European Ocean. This
species is frequently taken by the trawl-fishers in Plymouth
Sound. It has been found by M. d’Orbigny on the coasts
of France.
Genus Phoxichilus, Latr.—In this genus the palpi are
wanting, as in the preceding; but we observe a pair of
mandibles, and a greater elongation of the legs.
To this genus belongPycnogonum spinipes of the Fauna
Groenlandica, Phalangium hirsutum of Montagu (Linn.
Trans, ix.), Nymphon hirtum of Fabricius, &c.
Genus Nymphon, Fab.—Resembles the preceding genus
1 Recent observations induce the belief that these creatures breathe through their skins,_a peculiar character, which, when satis-
factonly established, may lead to their being erected into a separate order, intermediate in some respects between the Arachnides and
the apterous insects of the parasitical order. (See Rcgne Animal, tome iv. p. 277, note.)