Arachnids are prodigiously numerous.
In living Arachnids, excepting the Pantopoda, it is either fused (with loss of its appendages) with the prosoma (Limulus, 1 Scorpio), after embryonic appearance, or is 1 Pocock suggests that the area marked vii.
Ray's "Insects" comprised the Arachnids, Crustacea, Myriapoda and Annelida, in addition to the Hexapods.
- These most strange-looking Arachnids occur in warmer temperate, and tropical regions of Asia, Africa and America.
Their appearance in the air-breathing Arachnids does not separate those forms from the water-breathing Arachnids which are devoid of them, any more than does their appearance in certain Amphipoda separate those Crustaceans from the other members of the class.
The first of these has, in Arachnids as in other Arthropods, its pair of appendages represented by the eyes.
The second has for its pair of appendages the small pair of limbs which in all living Arachnids is either chelate or retrovert (as in spiders), and is known as the chelicerae.
The coxal glands do not establish any special connexion between Limulus and Scorpio, since thay also occur in the same somite in the lower Crustacea, but it is to be noted that the coxal glands of Limulus are in minute structure and probably in function more like those of Arachnids than those of Crustacea.
- Stra ussDiirckheim (1) was the first to insist on the affinity between Limulus and the Arachnids, indicated by the presence of a free suspended entosternum or plastron or entosternite in both.
They have appeared independently in connexion with a change in the excretion of nitrogenous waste in Arachnids, Crustacea, and the other classes of Arthropoda when aerial, as opposed to aquatic, respiration has been established - and they have been formed in some cases from the mesenteron, in other cases from the proctodaeum.
The fact that the single pair of prae-oral appendages of trilobites, known only as yet in one genus, is in that particular case a pair of uni-ramose antennae - does not render the association of trilobites and Arachnids improbable.
- Nomomeristic Arachnids, in which the somites corresponding to mesosoma and metasoma have entirely aborted.
The Epectinate Arachnids do not stand so close to the aquatic ancestors of the Embolobranchia as do the Pectiniferous scorpions.
Newport, George, " Nervous and Circulatory Systems in Myriapoda and Macrourous Arachnids," Phil.
Remains of air-breathing insects, myriapods and arachnids show that these forms of life were both well developed and individually numerous.
Oieape, a mite), a genus of Arachnids, represented by the cheese mite and other forms.
BOOK-SCORPION, or FALSE SCORPION, minute arachnids superficially resembling tailless scorpions and belonging to the order Pseudoscorpiones of the class Arachnida.
(London, 1900), and " On a collection of Insects and Arachnids " in Proc. Zool.
Other large Arachnids have not been derived from the scorpions directly, but have independently developed from aquatic ancestors, and from one of these independent groups - probably through the harvest-men from the spiders - the Acari have finally resulted.
For a longer or shorter period of their lives ticks are parasitic upon vertebrate animals of various kinds; but although the belief that the bite of certain tropical species is poisonous has long been held by the natives of the countries they infest and has been recorded with corroborative evidence by European authors in books of travel, it is only of recent years that accurate information has been acquired of the part played by these Arachnids in transmitting from one host to another protozoal blood-parasites which cause serious or fatal diseases to man and other animals.
Hexapoda and Arachnida); the penultimate joint with a process equal in length to the last joint, so as to form a nipping organ (chelae of Crustaceans and Arachnids); the last joint reflected and movable on the penultimate, as the blade of a clasp-knife on its handle (the retrovert, After Lankester, Q.
These are the plate-like swimmerets and opercula of Gigantostraca and Limulus among Arachnids and of Isopod Crustaceans.
It is possible, as maintained by some writers (Patten and others), that the lobes of the cerebral nervous mass in Arach nids indicate a larger number of prosthomeres as having fused in this region, but there is no embryological evidence at present which justifies us in assuming the existence in Arachnids of more than two prosthomeres.
In the Hexapods and Chilopods, and the Arachnids (usually), they form tree-like branching structures, and their finest branches are finer than any blood-capillary, actually in some cases penetrating a single cell and supplying it with gaseous oxygen.
Wasmann, who has compiled a list of nearly 1 50o species of insects, arachnids and crustaceans, inhabiting ants' nests.
The science of insects began with Aristotle, who included in a class "Entoma" the true insects, the arachnids and the myriapods, the Crustacea forming another class ("Malacostraca") of the "Anaema" or "bloodless animals."