THE 



ABACETUS. A genus of insects belonging to 

 the order Co/cop/n-a, family Ctirahidie. The antennae 

 are filiform, rather lengthened, and slightly com- 

 pressed: palpi with the last joint lengthened, almost 

 cylindrical, and truncated at the extremity : mandibles 

 somewhat porrected, slightly curved, and pointed : 

 the mentum with three lobes, the intermediate one 

 rounded : thorax trapezoid, almost as broad at the 

 base as the elytra : elytra long, rather narrow towards 

 the extremity, and rounded: anterior tarsi with the 

 first three joints dilated in the male, broader than 

 long, and triangular or cordiform. The Count de 

 Jean has established the above genus in the third 

 volume of his Species generate? des Cotioptercs, and has 

 described four species, all of which are found in 

 Senegal. 



AB ARTS. A genus of insects of the order Coleop- 

 tera, family Carabidtc. The antenna; are rather short, 

 slightly compressed, and almost filiform : labrum or 

 superior lip nearly square, or rather broader than 

 long : mandibles rather porrected, slightly curved, and 

 pointed : palpi, with the last joint cylindrical, and 

 truncated at the extremity : mentum notched, with a 

 simple and almost obtuse tooth in the middle : head 

 triangular : eyes large and very prominent : thorax 

 square: elytra long and oval: anterior tarsi, with 

 the first three joints dilated in the males, as long as 

 broad, and nearly triangular. Only one species of 

 this genus has yet been found ; it was sent to De Jean 

 from Carthagena, by M. Lebas. 



ABAX. A genus of insects belonging to the order 

 Coleoptcra, family HnrpaMa: (Carabns of Linnams) ; 

 the generic characters of which are, body broad and 

 depressed ; elytra united, or soldered together ; the 

 shoulders carinated, plicate, with no impressed dis- 

 coidal punctures ; wings none ; thorax transversely 

 quadrate, at the base on each side with two longitudi- 

 nal striae, the basal angles straight ; antennae setaceous, 

 and rather longer than the thorax, after the first four 

 joints hairy; palpi with their last joint oval; lip with 

 the tooth of its notch bifid ; anterior tarsi of the males 

 with three dilated joints. 



To this genus, which was established by the late 

 Professor Borelli of Turin, belongs the Carabm 

 striola of Fabricius, an insect not uncommon in this 

 country, in the spring of the year ; they are found 

 beneath stones, and sometimes under the bark of trees. 

 Abeu' metal liens has once occurred in this country, the 

 identical specimen is in the collection of J. H. Gries- 

 bach, Esq. The Count de Jean enumerates fifteen 

 species of the genus, most of which are found on the 

 continent. 



NAT. HIST. VOL 1. 



ABDOMEN. This term is generally understood 

 by naturalists as descriptive of a portion of the animal 

 structure somewhat analogous to the third and last, 

 great division of the human frame, though, in some 

 cases, a similarity of form and situation has alone 

 occasioned the adoption of that name. So long, how- 

 ever, as we confine the name of abdomen, as above 

 described, to animals of the class Mammalia, it is 

 perfectly correct. As the Mammalia and Birds, in the 

 principles of their formation, require a provision to be 

 made for an extraordinary exercise of bodily activity, 

 and particularly of rapid circulation and respiration, 

 they are furnished with an apparatus capable of power- 

 fully inflating the interior of their lungs ; at the same 

 time, the thoracic organs are found insulated from 

 the abdominal viscera, and the cavity of the latter 

 is perfectly circumscribed and well defined. But with 

 reptiles and fishes (still speaking of vertebrated 

 animals), the arrangement of the organ is found 

 to be changed, according to the different conditions 

 of their existence. In the first, one simple cavity 

 encloses the respiratory, circulatory, and digestive 

 organs. If from the vertebrated, we pass to the inverte- 

 brated animals, we shall not find in them any cavity to 

 which the name of abdomen can properly apply, as 

 being receptacles formed of the same elements and 

 inclosing the same viscera. With these the organs of 

 circulation, respiration, and digestion, no longer occupy 

 distinct cavities; to neither molluscous animals, 

 worms or annelides, can we properly attach the terms 

 thorax and abdomen, as they are defined in the human 

 anatomy. 



In the Arachnids the continuation of the thorax is 

 called the abdomen ; and no doubt has arisen as to its 

 analogy with the abdomen of insects. It may, how- 

 ever, be observed, that the resemblance only holds good, 

 inasmuch as it forms a continuation of the thorax, and 

 contains a portion of the intestinal canal ; but not 

 because it is formed of the same rings, or because it, 

 encloses, without exception, the same viscera possess- 

 ing similar functions : observation proving that it is 

 not the same under every circumstance. 



In the hexapodal insects the abdomen is well de- 

 veloped, perfectly distinct from the thorax, particularly 

 when that part supports the wings, for in the apterous 

 individuals, that difference is, in default of these organs, 

 rather less marked; the same may be said of the 

 greater number of larvae, all of which, having the rings 

 of the body equally developed, cannot be divided into 

 abdomen and thorax, if the existence of feet to the 

 three first rings did not sufficiently indicate the respec- 

 tive limits of each of them. It, is, nevertheless, i;n- 

 B 



