TRACHEARIiE. 



4/1 



or rounded, and generally soft : in some males, it is narrowed behind into a cylindrical tail. The 

 number of eyes is either two or four, and even six, according to Muller. 



Eijlais, Latr., has the chelicerae terminated by a moveable claw. A. extendcns, Fabr. 



Hydrachna, Latr., has the mouth composed of plates, formiiiap a projecting 

 sucker, and the palpi have a moveable appendage beneath the extremity. 

 A. geograpMcus, Fabr., A. glohator, Fabr. 



Limnocharcs, Latr., has the mouth sucker-shaped, but the palpi are simple. 

 A. aquaticiis, Linn. [Other species of these water-mites have been described 

 by M. Theis, in the Annales des Set. Nat. for 1832]. 



[From the very valuable discoveries lately made by M. Dug&s, it appears 

 that these water-mites undergo metamorphoses, accompanied by a complete 

 change of form, the larva; having a very large head and six legs, whilst the 

 pupae are inactive, attaching themselves, by a single pair of legs, to the 

 bodies of other aquatic insects, and consisting, as it were, simply of an oval 

 hag with a narrow neck, the insect in this state having been formed, by 

 M. V. Audouin, into the genus Achlysia, and specifically named A. Dt/tici, from taking up its residence beneath 

 the elytra of the Water Beetle {Dyticus marginalis). They also attach themselves to the slender filaments com- 

 posing the tails of the Water Scorpions (Nepa and Ranati-a).] 



Other Mites (Micropthira, Latr.) differ from all the foregoing, in having six legs. They are all parasites. 



Caris, Latr., has the sucker and palpi distinct; the body rounded, very flat, and covered with a scaly skin. C. 

 vespertilionis, Latr. On Bats. 



[M. V. Andouin has figured an insect which he considers may be identical with Caris vespertilionis, in the 

 Annales des Set. Nat., 1832 ; and which, notwithstanding its possessing only six legs, he considers as more pro- 

 perly belonging to the genus Argas.] 



Leptiis, Latr., has also a sucker and palpi, but the body is soft and ovoid. A. autitmnalis, Shaw {Misc. Zool., 

 vol. ii. pi. 42), is very common, in autumn, upon grass and other herbage. They crawl upon our bodies, and in- 

 sinuate themselves into the skin at the roots of the hairs, occasioning as painful an irritation as the itch. [It is 

 the well-known Harvest Bug], but it is so minute as rarely to be observed. 



Tlie other species are found upon diffei-ent insects, and enter into the division of the Trombides hexapodes of 

 Hermann. T. insectorum, Herm., T. LibelluUe, Herm., T. Culicis, Herm., &c. 



[Aclysia, And., here placed by Latreille, is now proved to be the immature state of Hydrachna.] 



Atoma, Latr., has neither suckers nor palpi visible ; the mouth consists only of a small orifice, situated upon the 

 breast ; the body is soft, oval, with the feet short. Acarus parasiticus, Herm. 



Ocypete, Leach, belongs to this section, from the number of its legs ; but, according to him, it has mandibles. 

 O. rubra. Leach. Upon Tipulce. 



[From the recent observations of Audouin, Dugfes, and others, it seems questionable whether this terminal sec- 

 tion of the Mites can be retained, consisting, as it is now supposed to do, entirely of the young states of various 

 groups of Acaridae.] 



[The Senator Van Heyden has lately published a distribution of the Acaridae in the Isis ; and many very minute 

 species are figured in the continuation of Panzer's Fauna Insectorum Germanics, by Herrick Schaffer, distributed 

 into many new genera. At the same time, M. Dug^s, in his more elaborate and complete memoir, published in 

 the Annales des Sci. Nat., has revised the entire group, dividing it into numerous genera, arranged into the fol- 

 lowing groups:— 1. Trombidiei; 2. Hydrachniei; 3. Gamasei; 4. Ixodei ; 5. Acarei; 6. Bdellei; and, 7. Oribatei.] 



THE THIRD CLASS OF ARTICULATED ANIMALS FURNISHED WITH 

 ARTICULATED LEGS,— 



INSECTS (Insecta),— 



Which have articulated legs, a dor.sal vessel occupying the place of the vestige of a 

 heart, but without any branch for circulation * ; which respire by means of two principal 



♦ Anatomists are divided in their opinion as to the nature of this 

 organ, many regardinif it as a distinct heart, whilst others (including 

 Cuvier, wliosc opinion appears to have been fully confirmed by the 

 researches of M. de Serres, inserted in the M^inoirea du Mus. d'Uist. 

 Silt.) deny it this quality. Some recent observstions appear to esta- 

 blish the eiistence of several small vessels, but besides that, this cir- 

 culation must be Ter>- partial, as Insects differ matt-rially fri>m the 

 Crustacea, the blood not returninj; to the lieart. AccordiuK to Ilerold, 

 as quoted by Strauss {liutletin. dt Univert Ferusiac), the dorsal vessel 



is the true heart of insects, being, as in the higher animals, the loco- 

 motive organ of the blood, which, instead of being ci>ntained in vessels, 

 extends through the general cavity of the body. This heart occupies 

 the entire length of the bulk of the abdomen, and terminates ante- 

 riorly in a single artery, which is not ramified, and which carries the 

 blootl to the head, whence it returns to the abdomen by the mere 

 effect of its accumulation in the head, (o re-enter the heart ; and it is 

 in this that the entire circulation of the blood of insects consists, and 

 which are consequently destitute of veins. According to M. Slratss. 



