452 
ARTICULATED ANIMALS. 
[It is to be observed, that these two orders are regarded by various celebrated || 
naturalists as too widely distinguished from each other to remain in the same class, m 
This idea was first entertained by Dr. Leach, (Zoological Miscellany, vol. iii. 1817), || 
who restricted the class to the families Scorpionidse, Tarantulidee, Phalangidee, Solpu- | 
gidse, and Araneidae, all of which were assumed to breathe by means of pulmonary 
sacs, whilst the Trachearia of Latr. (excepting the Pycnogonidae and Phalangidae), J 
were formed into a separate class, which he proposed to name Acari. Even Latreille 
himself, in his Cours d’Entomologie, thought it necessary to separate the Pycnogonides I 
into a distinct order of the class Arachnida, which he named Aporobranchia. | 
Messrs. Kirby and Spence (Introd, to Entomology, vol. iii. p. 21) were also of opinion r| 
that the Pulmonary and Trachean Arachnida should not be included in the same class ; ; 
but Mr. MacLeay (Horce Entomologicce, p. 382) maintained that the diversity of the | 
organs of respiration and circulation is not to be depended upon in the classical arrange- ;! 
ment of the Annulosa ; and more recently Duges, in his memoir upon the Acari, 
adopted a similar view, considering that external form and general coincidence of 
characters, such as the presence of eight feet for walking, the absence of organs used 1 1 
as antennse and reticulated eyes, and the constant union of the head and thorax, are of ; 
more importance than the variations in the organs of respiration and circulation. This, ‘ 
which I consider as the most philosophical view of the subject, (confirming as it does 
my observation on the distribution of the Crustacea proposed by M. Duverney, anfh, ‘ • 
p. 410, note,) has been still more recently confirmed by Duges, who has read a memoir, : 
before the French Institution, in which the genera Dysdera and Segestria, belonging 
to the Spiders, are stated to possess four spiracles, two of which are connected with ,, 
pulmonary, and two with trachean organs (see Guerin, Bull. ZooL, No. 2). This | 
author has illustrated this structure in the Crochard edition of the Regne Animal,^ 
livr. 10, Arachnides, pi. 10, f. 4. With the view of adapting the arrangement of Leach f 
to that of Latreille, I have proposed the following distribution of the class (Ent. Text I 
Book, p. 131). ;! 
Section I. Pulmonaria, Latr. [ 
Order 1. Dimerosomata, Leach, Araneides, Latreille. 
Order 2. Polymerosomata, Leach, Pedipalpi, Latreille, {Scorpionida and Phrynida).i 
Section II. Trachearia, Latr. | 
Order 3. Adelarthrosomata, Westw., composed of the families Solpugida, Cheli-^ 
feridce, and PhalangiidcB. \ 
Order 4. Monomer osomata, Leach, restricted to the Acari. 
Section III. Aporobranchia, Latr. 
Order 5. Podosomata, Leach, consisting of the single family Pycnogonides. 
The Baron Walckenaer, in his valuable Histoire Naturelle des Insectes Apt^res,^ 
(Paris, 1837, 8vo, tom. i.), has divided the Arachnida of LatreiUe, which he names . 
Aceres, after Lamarck, (not adopting the views of Latreille that the chelicerse are modi- jj 
fied antennae), into six orders 1 . The Araneides (Theraphoses and Araigne'es) 
2. Phryneides (Phrynus, Thelyphonus) ; 3. Scorpionides (Scorpio, Chelifer, and 
Ohisium) ; 4. Solpugides (Galeodes) ; 5. Phalangides (Phalangium, Siro, Macro^ 
cheles, Trogulus, and Mites”) \ 6. Acarides (Tromhidium, Hydrachna, Gamasus, 
Ixodes, Acarus, Eylais, Bdella, and Orihata). Thus we find that the respiratory organs 
