ARACHNIDA. 
451 
by a pectoral elongation ; two maxiUse, formed of the basal joint of two small feet 
or palpi *, or of an appendage or lobe of the same joint ; a piece concealed beneath 
the mandibles, and called the sternal tongue by Savigny in Phalangium copticum, 
and which is composed of a beak-like prominence, produced by the union of a very 
small epistome or clypeus, terminated by a very small triangular upper lip, and of 
a longitudinal lower rib {carene) generally very hairy. These, together with the pieces 
called the mandibles, generally constitute, with certain modifications, the mouth of the 
majority of the Arachnida. The pharynxf is placed in front of a sternal prominence, 
which has been considered as a lip, but which, from its situation immediately in front 
of the pharynx, and from being destitute of palpi, is rather a tongue. The legs, like 
those of the Insecta, are generally terminated by two small hooks {ungues) and 
sometimes by an additional one, and all are annexed to the thorax (or rather 
cephalo thorax), which, except in a few species, is only composed of a single piece, 
and very often intimately united to the abdomen, which is soft or but weakly 
defended in the majority. 
With respect to their nervous system, the Arachnida remarkably differ from the 
Crustacea and Insecta, for, if we except the Scorpions, which, in consequence of 
their articulated tails, have some extra ganglions, the number of these knots does 
not exceed three, and even in those animals there are only seven. 
The majority of the Arachnida feed upon insects, which they seize alive, or upon 
which they fix themselves, and from which they suck their juices. Others live as 
parasites upon the bodies of vertebrated animals. There are, however, some which 
are found only in flour, cheese, and upon various vegetables. Those which sub- 
sist upon other animals often increase in a very great degree. In some species two 
of the legs are not developed before a change of skin, and in general it is not 
until after the fourth or fifth moulting that these animals become fitted for repro- 
duction.! 
Those species which have pulmonary sacs§, a heart with very distinct vessels, 
and six or eight eyes, compose the first Order, Arachnida pulmonaria. 
The others respire by trachese, and do not possess organs of circulation; or, if 
they be present, the circulation is not complete. The trachese are divided near their 
origin into different ramifications, and do not form, as in the Insects, two canals, 
running parallel with the entire length of the body, and receiving the air in its 
different parts by numerous breathing pores. Here we can only distinctly perceive 
two II at most, situated near the base of the abdomen. The number of the simple 
eyes is four at the most. These form our second and last Order, Arachnida 
trachearia. 
* These organs do not dififer from true legs, except in their tarsi, 
composed of a single joint, and generally terminated by a small hook, 
similar to the ordinary legs of the Crustacea. These maxillae and 
palpi appear to correspond with the palpigerous mandibles of the 
decapod Crabs, and to the two fore-legs of Limulus ; the four follow- 
ing legs of Phalangium have a basal maxillary appendage, analogous 
to the four maxillae of the preceding animals, described by me in my 
I monograph of the French Phalangia, years before Savigny’s Memoirs 
were published. Hence it is easy to refer all these articulated 
animals to one general type, and hence the Arachnida are not a kind 
' of Crustaceous animals, destitute of a head, as Savigny says. 
I t M. Strauss and myself have only observed one orifice, although 
Savigny admits (but, as it seems to me, incorrectly) two. 
'! t We have also seen that the Argulus does not attain this power 
J until after the sixth moult. ITie same fact is also applicable to 
Lepidopterous insects, and probably to others which change their 
skins several times — thus. Caterpillars moult four times before 
assuming the chrysalis state, which is effected by a fifth moult, and 
the insect does not become an imago until after another, which makes 
six muultings. 
§ Sacs inclosing aerial branchiae, or performing the office of lungs, 
and which I distinguish from the latter organs by the name of pneumo- 
branchise. 
II The Pycnogonides are destitute of spiracles, and thus appear to 
approach the terminal Crustacea, such as Dichelestium and other 
Entomostraca suctoria. Savigny considers them most allied to the 
Ltemodipodous Crustacea, from which, however, they widely differ in 
the structure of the mouth, eyes, and legs. We believe them to be- 
long rather to the class Arachnida, near to Phalangium, considering 
they may respire by the surface of their skin. 
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