TO THE ARTICULATED ANIMALS. 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.] 



ARTICULATED ANIMALS, FURNISHED WITH ARTICULATED FEET.* 



IN GENERAL. 



CRUSTACEA, ARACHNIDA, AND INSECTA. 



These threef classes, united together by Linnaeus 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 cniiiitttr«'d to a skeleton, or vertebral column ; but this 

 is erroneous, because the supposed %"ertebrx are only hardened por- 

 tions of the skin, connected by more slender membranous intervening 

 portions. The researches of Stiauss especially prove this, in .opposi- 

 tion to Robineau Pesvoidy, and others. The power of exuviation 



t Hexapods. Those with more than six feet »rt the Apiropoda of 

 Savigiiy, or my Hyperhexapods. 



§ In many Crustacea, the second piece of the coxa appears to form 

 part of the femur, and the tibia (as also in the Arachnida) are two- 

 jointed. 



According to M. Odier, the chief snbstance of which this integu- 



espcciilly distintruishes these from other lovertebrata. | ment is composed is of a peculiar nature, which lie names chitine. 



t Dr. Le:\ch formed the Myriapoda into a distinct class. The tra- 

 cliean .Arachnida might also, from their anatomical characters, consti- 

 tute another, but they are too nearly allied to the puluior.ary Arach- 

 nida tc %llow this separation. I 



Phosphate of lime forms the chief part of the salts of the teguments 

 of insectSt m hilst the carapax of the crabs abounds in carbonate of 

 lime. 



