Order 2. 



TRACHEARLE. 



471 



Fig. 41. — a, Hydrachiia globulus 

 fied ; c, young l:irva ; d, pupd,. 



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. 



Eylais, Latr., has the chelicerae terminated by a moveable claw. A. extcndens, Fabr. 



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

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

 A. geographiciis, Fabr., A. globntor, Fabr. 



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

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

 by >L Theis, in the Annales des Sci. Nat. for 1832]. 



[From the very valuable discoveries lately made by M. Dugfes, it appears 

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

 change of form, the lan'ae having a very large head and six legs, whilst the 

 pupae 4re inactive, attaching themselves, by a single pair of legs, to the 

 mas"'- bodies of other aquatic insects, and consisting, as it were, simply of an oval 

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

 M. V. Audouin, into the genus Achlysia, and specifically named A. Dytici, 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 (Aepa and Ranaira).} 



OtherMites {Micropthira, Latr.) differ from all the foregoing, in having six legs. They are all parasites. 



Carts, 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 Sci. 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. autumnalis, 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. 



The other species are found upon different insects, and enter into the division of the Trombides hexapodes of 

 Hermann. T. insectoritm, Herm., T. Libellitlte, Herm., T. Citlicis, Herm., &c. 



[Aclysia, Aud., 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. Acarits parasiticus, Herm. 



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

 O. rubra. Leach. Upon Tipuls. 



[From the recent observations of Audouin, Dug^s, 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 Germanite, by Herrick Schafier, distributed 

 into many new genera. At the same time, M. Duges, 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:—!. 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 dorsal 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 opiniun as to the nature uf this 

 organ, many regarding it as a dj.stinct heart, whilst others (including 

 Cavier, wliose opinion appears to ha%'e been folly confirmed bv the 

 researches of M. de Serres, inserted in the M^moires dtt Mus. d'Hist. 

 Nat.) deny it this quality. Some recent obser^'Stiuns appear to esta- 

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

 ciiiatiun must be very partial, as Insects differ materially from the 

 Crustacea, the blood not returning to the heart. According to Herold, 

 ita qaoled by Slrausi {Bulletin, de Univer$ Ferustac), the dorsal vessel 



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

 motire organ of the blood, which, instead of being contained in vessels, 

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

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

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

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

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

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

 which are conftequently destitute cf veins. According to M. StracKS. 



