Polypods. This suborder consists of Dr. Leach's Class Myriapoda, or the Chilognatha and Chilopoda of Latreille, corresponding with the Linnean genera Iulus and Scolopendra. Mr. MacLeay has arranged them in the same Class with the Hexapods, and connects them with the Anoplura by means of certain intestinal worms of an indistinct annulose structure[1244] (Entozoa Nematoidea Rud.), in which the sexes are diœcious, and some of which are furnished with lateral spinulæ,—thus, as he supposes, connected with the Polypods; and with the Anoplura by others (Epizoaria Lam.) in which appendages appear somewhat analogous to the legs of Hexapods, as in Cecrops Leach, and which like them are parasitic animals[1245]. But the right of these worms to be considered as members of the same Class with the Hexapods and Polypods at present appears rather problematical, and requires further examination.
Def. Metamorphosis subcomplete[1246].
Body consisting of numerous segments.
Mouth perfect[1247].
Eyes compound or aggregate.
Antennæ distinct.
Legs six on the trunk, many on the abdomen.
I must next say something on the Orders of the Arachnida. Every one, at first sight, sees that spiders and scorpions are separated by characters so strongly marked, that they look rather like animals belonging to different Classes than to the same: these form the two primary Orders of the Arachnida, and they appear to be connected by two secondary or osculant ones,—on the one side by Galeodes, and on the other by Thelyphonus and Phrynus[1248]. This Class, although there is an appearance of eight legs, is, strictly speaking, of a Hexapod type; for the anterior pair, ordinarily regarded as legs and performing their function, are really the analogues of the maxillary palpi of perfect insects. This will be evident to you if you examine any species of Galeodes. These animals, if we look at them cursorily, we should regard as Decapods; but when we trace the two anterior pairs of apparent legs to their insertion, we find that both proceed from the head, which in that genus is distinct from the trunk; while the three last pairs, which alone are furnished with claws, are planted, as legs usually are, in the latter part. The first pair represent the ordinary palpi of Arachnida, are analogous to the labial ones of Hexapods, and, as likewise in Phrynus and Thelyphonus, are more robust than what are usually taken for the first pair of legs; but they differ in being considerably longer, and instead of terminating in a chela are furnished with a retractile sucker[1249]. The second pair are more slender and shorter than the first; they correspond precisely with what are deemed the first pair of legs of Octopods and Arachnida, and are clearly analogous to the maxillary palpi of perfect insects. Whether the base of the first pair of these palpi is in any respect analogous to the labium of insects, (as that of the second seems to be to their maxillæ,) I am not prepared to assert: it will therefore be most advisable to name these palpi anterior and posterior: but as they evidently proceed from the head in Galeodes, and in that genus are clearly analogous to those of the Phrynidea, (which in their turn as clearly represent those of the Aranidea,) it follows that in all they are organs of the part representing the head, and therefore not in a primary sense legs; although in a secondary, as M. Savigny has proved, they may be so called[1250].
1. Araneidea McL. (Aranea L., Araneidæ Latr.) The Araneidea, or spiders, seem resolvable into two suborders,—the Sedentaries and the Wanderers; thus forming, perhaps, what Mr. MacLeay would denominate the normal groups of a circle of Arachnida.
Def. Mandibles armed with a perforated claw.