466 



4.RACHNIDA. 



mined. Each of the four following segments has a pair of pulmonary sacs and spiracles. Immediately after the 

 sixth segment, the abdomen is suddenly narrowed, the six terminal knotted joints forming the tail. The tarsi are 

 alike, and 3-jointed, with two terminal ungues. The two nervous cords running from the brain are united at in- 

 tervals, forming seven ganglions, of which the terminal ones belong to the tail. For further details of the anatomy 

 of these animals, consult the works of Treviranus, M. de Serres, and Leon Dufour (Jouru. de Physique, 1817). 



These Arachnida inhabit the warm countries of both hemispheres, living in the ground, hiding themselves 

 under stones or other bodies, generally amongst ruins, or other dark and cool places, and even in the interior of 

 houses. They run quickly, and curve the tail over the back. Tbey can turn it in all directions, and employ it as 

 an arm of defence or offence. They seize Wood-lice, and other ground insects, such as Carabi, Weevils. Ortho- 

 ptera, &c, which serve them as food, with their pincers, pricking them with their stings, and then carrying them 

 to their mouth. They are also particularly fund of the eggs of Spiders and other insects. 



The wound occasioned by the sting of the Scorpio europaus is not, as it appears, ordinarily dangerous. That 

 of the Scorpion of Souvignargues, of Maupertuis, or of the species which I have named Occitanus, and which is 

 more powerful than that of the preceding, produces, according to experiments which Dr. Maccary had the courage 

 to try upon himself, more alarming effects. The poison appears to increase in power according to the age of the 

 animal. Volatile alkali, either applied interiorly or exteriorly, is used to counteract its effects. 



Some authors assert that the indigenous [French] species produce two broods in a year, but it appears more 

 correct to consider that this takes place in the month of August. According to Maccary, it changes its skin before 



coupling. The female carries her young upon her back for 

 several days, at first not quitting her abode at such time, and 

 takes care of them for the space of a month, by which time 

 /£jj s^S they are able to shift for themselves. 



Some have eight eyes, forming Leach's genus Buthut. 

 Scorpio afer, Linn., which is five or six inches long, and in- 

 habits the East Indies, Ceylon, &c. S. occitanus, Amoroux, 

 (Titnt'tanus, Herbst.) Middle of Europe, Barbary, Spain, &c. 

 The others have only six eyes, forming the restricted genus 

 Fig. 32 -Scorpio occitanus. Scorpio of Leach. S. europaus, Linn., Fab., Herbst. South 



of France. 

 [The genus Scorpio, Linn., has been revised by Hemprich and Ehrenberg in their great work upon the animals 

 of Arabia, and many new genera and subgenera separated therefrom. Many new species have also been recently 

 described by Koch, in the continuation of Halm's Die Arachniden.] 



THE SECOND ORDER OF ARACHNIDA — 



TRACHEARIJS,— 

 Differs from the preceding in the respiratory organs, which consist of radiating or ramified 

 tracheae*, which only receive the air by two spiracles; in the absence of a circulating organ f, 

 and in the number of the eyesj, which is only two or four. From the want of sufficiently 

 generalized anatomical observations, the limits of this order are not rigorously determined. 

 Some species, indeed, of these Arachnida — such as the Pycnogonidce — do not exhibit any 

 spiracles ; and their mode of respiration is unknown. 



The trachean Arachnida are naturally divisible into those provided with chelicerse terminated 

 by two fingers, one of which is moveable, or by a single one, equally moveable, in the form of 

 a hook, and those where these organs are replaced by simple plates or lancets, which, together 

 with the tongue, compose a sucker ; but the majority of these animals being minute, their 

 examination is attended with very great difficulties, so that these characters ought only to be 

 resorted to when it is impossible to adopt others. 



* The trachea; are vessels which receive and distribute the aerial 

 fluid in every part of the interior of the body, and thus remedy the 

 want of circulation. They are of two kinds, — tubular or elastic (formed 

 of three membranes, the middle one composed of a spiral thread), and 

 vesicular, formed of only two membranes these form a kind of pneu- 

 matic reservoir, capable of inflation, communicating with each other 

 by means of tubular tracheee. The tracheae are divided into two prin- 

 cipal trunks, extending along the sides of the body, and receiving the 

 sir by orifices or spiracles. There are also, in many insects, two other 

 longitudinal trunks, situated between the preceding, with which they 

 communicate, and which Serres calls pulmonary trachea, giving to 

 the ordinary ones the name of arterial tracheae. He also distinguishes 

 tue kiud of spiracles : the common ones are closed by membranous 

 lips, opening by simple contraction the others, named treuiaeres by 



Serres, are shut by corneous, moveable plates, and are peculiar to 

 some Orthoptera. Some aquatic larvae have a very peculiar respiratory 

 apparatus. 



t The presence of tracheae excludes all complete circulation, — that 

 is, the distribution of the blood to different parts, and its return from 

 the organs of respiration to the heart. Hence, although certain vessels 

 have been discovered in some insects (Phasmte), and their existence 

 is possible in the trachean Arachnida, these creatures do not the less 

 enter into the general system, M. M. de Serres has observed that the 

 intestinal canal of Phalangium emits a very great number of ccecums, 

 or vermiform appendages, which appear analogous to hepatic vessels, 

 and that the tracheae ramify most extensively upon these ccecums. 



t According to Miiller, Hydrachna umbrata has six eyes ; but is not 

 this a mistake? 



