ARTICULATED ANIMALS. 
r 
405 
them, with certain worms, into a class, for which he adopted Leach’s name, Ameta- 
bola (changeless), in order to distinguish them from the true insects, which undergo 
transformations. This author retained the classes Crustacea and Arachnida, but di- 
vided the insects, from the structure of their mouth-organs, into those with mandibles 
and those with a suctorial mouth, — characters which we have seen had been employed 
in the arrangement of the orders of insects inter se. 
Other arrangements have been proposed by Kirby and Spence, Burmeister, &c., to 
which I can but refer. — I shall, therefore, only add that it appears to me most natural 
to confine the Ametabola to the Myriapoda, Thysanura, and Anoplura ; to unite the 
winged insects into one class, named Ptilota, after Aristotle ; and to retain the Crustacea 
and Arachnida in the limits here detailed. — Entomol. Text-Book, p. 79 ; and Introd. 
to Modern Classific. of Insects, vol. i. p. 4.] 
f ARTICULATED ANIMALS, FURNISHED WITH ARTICULATED FEET,* 
J IN GENERAL. 
CRUSTACEA, ARACHNIDA, AND INSECTA. 
These threef classes, united together by Linnseus under the common name of Insects, 
but which I name Condylopa, are distinguished by their articulated feet, of which they 
have at least six.J Each joint [of the legs] is tubular, and contains the muscles of the 
following articulation, which always moves by ginglymus, — that is, in but one direc- 
tion. The first joint which attaches the limb to the body, and which is generally com- 
posed of two§ pieces, is named the coxa, or hip, [the second of these pieces, when 
present, is termed the trochanter] ; the next piece, which is ordinarily in a position 
nearly horizontal, is the femur, or thigh ; the third is generally vertical, and is named 
the tibia, or shank ; and the terminal part of the leg, or properly the foot, is composed 
of a series of small joints, which touch the ground, and which are collectively named 
the tarsus. ' 
The hardness of the calcareous or horny || envelope of the majority of these animals 
is owing to that of the excretion which is interposed between the dermis and epidermis, 
or what is termed in Man the mucous tissue. It is also in this excretion that are lodged 
the often brilliant and varying colours with which these animals are sometimes adorned. 
These creatures are always furnished with eyes. These are of two kinds : — 1st, The 
simple eyes, named ocelli, or stemmata, ordinarily resembling a minute lens, and of which 
there are generally three, arranged in a triangle on the crown of the head ; and, 2ndly, 
the facetted or composite eyes, of which the surface is divided into an infinite number of 
* The series of [external] articulations of which the body is com- 
posed has been compared to a skeleton, or vertebral column ; but this 
is erroneous, because the supposed vertebras are only hardened por- 
tions of the skin, connected by more slender membranous intervening 
portions. The researches of Strauss especially prove this, in opposi- 
tion to Robineau Desvoidy, and others. The power of exuviation 
especially distinguishes these from other Invertehrata. 
t Dr. Leach formed the Myriapoda into a distinct class. The tra- 
chean Arachnida might also, from their anatomical characters, consti- 
tute another, but they are too nearly allied to the pulmonary Arach- 
nida to allow this separation. 
t Hexapods. Those with more than six feet are the Apiropoda of 
Savigny, or my Hyperhexapods. 
§ In many Crustacea, the second piece of the coxa appears to form 
part of the femur, and the tibiae (as also in the Arachnida) are two- 
jointed. 
II According to M. Odier, the chief substance of which this integu- 
ment is composed is of a peculiar nature, which he names chitine. 
Phosphate of lime forms the chief part of the salts of the teguments 
of insects, whilst the carapax of the crabs abounds in carbonate of 
lime. 
