TRACIIEARI^. 



471 



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 Miiller. 



Eijhfi-s, Latr., lias the chelicera: terminated by a moveable claw. A. extendens, Fabr. 



Nij(lrackfia,hatr., has the mouth composed of plates, founhiz a projecting 

 sucker, and the palpi have a moveable appendaj^-e beneath the extremity. 

 A. geugrapMcus, Fabr., A. glohator, Fabr. 



Li iimo chares, Latr., has the mouth sucker-shaped, but the palpi are simple. 

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

 by M. Theis, in the Annates des Sci. Nat. for 18:J2]. 



[From the very valuable discoveries lately made by M. Du3;t*s, it appears 

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

 chaiif^e of form, the lan'a havin;^ a ^'ery large head and six legs, whilst the 

 \m\iii- are inactive, attaching themselves, by a single pair of legs, to the 

 bodies of other aquatic insects, and consisting, as it were, siniply 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. Di/tic?y from taking up its residence beneath 

 the elytra of the Water Beetle (Z>.v^i6'»if maj-f/iHa^w). They also attach themselves to the slender filaments com- 

 jiosing the tails of the Water Scorpions {Ncpa and Ranatra).'] 



Other Mites {Micropthira^l^QAv.) differ from all the foregoing, in having six legs. They are all parasites. 



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

 re,y)cr(ilion/6\ Latr. On Bats. 



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

 Annah's des ScL Nat., 1832 ; and which, notwithstanding its possessing only six legs, he considers as more pro- 

 perly belonging to the genus Argas.] 



Leplm; Latr., has also a sucker and palpi, but the body is soft and ovoid. A. autumnalis, Shaw (Mise. 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 sjiecies are found upon ditlerent insects, and enter into the division of the Trombides hexapodes of 

 Hermann. T. insectorum, Herm., T. Llhellula, Herm., T. Culicis, Herm., &;c. 



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



Atoina, 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. Acarns parasiticus, Hcnn. 



Oci/pcte, Leach, bL-Iongs to this section, from the number of its legs ; but, according to him, it has mandibles. 

 0. rubra, Leach. Upon Tipulas. 



[Urom 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 Acarida'.] 



[The Senator Van Ileyden has lately published a distribution of the AcaridK in the Isis ; and many vei-y minute 

 species are figured in tiic continuation of Panzer's Fauna Insectorum Germauice, by Herrick SchaftVr, 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. liydrachniei ; 3. Gamasei ; -t. 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 



■of this 

 icludiuu 



s to have bL-cn fully confirmed by the 

 isertetl in the AUinoirea du Mus. d'J/ht. 



^ Anatomists are divided in their opinion as to the na 

 orgnn, many regnrdin|i; it as a distiiiet heurt, M'hilst oilier 

 Cuvier, wiiosc oiJinion ftppe;; 

 reseiirchca of M. de Serres, 

 Nat.) deny it this qurtlity. Some recent observations appear to esta- 

 blish the existence of several smaH vessels, but besides tbat, this cir- 

 cuUitiufi must be very piirlial, as Insects differ materially from the 

 Cr'isiacea the blood not retiirnini,' to the heart. Accordinu to Hcrold, 

 as quoted by Strauss [Bullelin. de Univert FcTUSsac), the dorsal vessel 



is the true heirt of insects, being^, as in the hii^her nnimftia, the loco- 

 motive organ of ihe blood, which, insteari of being contained in vessels, 

 exteniis throujjh the general cavity of the body. This heart occupies 

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

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

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

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

 in this that the entire circulation of the blood of insects coiisii^ts, and 

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



