ANNELIDES. 
389 
in species of any throughout the Animal Kingdom. With the exception of some 
genera (the Myriapoda), which have the body divided into a great number of subequal 
articulations, they all consist of three parts : the head, upon which are the antennae, 
the eyes, and the mouth ; the thorax or corselet, which bears the feet, and the wings 
whenever these exist ; and the abdomen, which is suspended to the thorax, and con- 
tains the principal viscera. Insects that have wings do not possess these [externally] 
before a certain age, and often pass through two forms or stages, more or less different, 
before they assume the winged state. They respire in all these states by means of 
tracheae, which are elastic vessels that receive the air by orifices termed stigmata, 
pierced in their sides, and which are distributed by minute ramifications over every 
part of the body. The only vestige of a heart consists of a vessel which runs along the 
back, and alternately contracts along its course, but to which no branches have been 
discovered : hence it is believed that the nutrition of the several parts is effected by 
imbibition ; and it is probably this mode of deriving the nutriment which necessitates 
the kind of respiration proper to these animals, the nourishing fluid not being con- 
tained in vessels*, wherefore, as there was no means of directing it towards cir- 
cumscribed pulmonary tubes to be aerated, the latter are consequently diffused over 
the whole body, instead. Thus it is, also, that Insects have no secretory glands, 
but merely long spongy vessels, which appear, over their whole surface, to absorb the 
several juices that should produce them, from out of the mass of nutritive fluid. f 
Insects vary endlessly in the form of their manducatory and digestive organs, as also 
in the industry of their habits, and mode of life. Their sexes are always separate. 
The Crustaceans and Arachnides were long confounded with them under a common 
name ; and in many respects bear a considerable resemblance to them, in external form, 
the disposition of their organs of movement, their sensations, and even manducation. 
THE FIRST CLASS OF ARTICULATED ANIMALS,— 
THE ANNELIDES,— 
Are the only Invertebrate Animals that have red blood : this circulates in a double 
system of complex vessels. Their nervous system consists of a double nervous chord, 
the same as in Insects. Their body is soft, more or less lengthened, and often divided 
into a very considerable number of segments, or at least of transverse folds. 
Almost all of them (the Earth-worms excepted) live in water. Many bury them- 
selves in holes at the bottom, or construct for themselves tubes of mud and other 
matters, or even transude a calcareous substance, which forms a sort of tubular shell. 
DIVISION OF THE ANNELIDES INTO THREE ORDERS. 
This class, not a, very numerous one, offers in its respiratory organs the basis of 
three sufficient divisions. 
Some have their branchiae in form of tufts or arhuscules, attached to the head, or 
• M. Carus has observed various movements in the fluid which fills | ^c., in German. Leipsic, 1827, 4to. 
the body of the larvae of certain Insects ; but these movements do not I |- See, upon this subject, my Memoir on the Nutrition of Insects, 
take place in a system of closed vessels, as in the higher animals. — 1 printed in 1799, among those of the Natural History Society of Paris 
See his Treatise, iutitled Discovery of a simple Circulation of Blood, j Baudouin, An vii. 4to, p. 32. 
