OCR Text |
Show 58 INSECTA. riegated colours with which they are adorned, their large wings resembling lustrous gauze, and the velocity with which they pursue the Flies, &c., that constitute their food, attract our attention and enable us to recognize them with facility. Their head i~ large, rounded, or in the form of a broad triangle. They have two great lateral eyes( 1) and three simple ones situated on the vertex; two antennre, inserted into the forehead behind a vesicular prominence, composed of five or six joints, or at least of three, the last of which is compound and attenuated in the manner of a stylet; a semi-circular arched labrum; two very strong, dentated and squamous mandibles; maxillre terminated by a piece of the same consistence that is dentated, spinous, and ciliated on the inner side, with a uniarticulated palpus laid on the back and representing the galea of the Orthop· tera; a large, arched, trifoliate labium, of which the two lateral leaf· lets are pal pi; a sort of epiglottis or vesicular and longitudinal tongue in the interi01· of their mouth; a thick and rounded thorax; a highly elongated abdomen which is sometimes ensiform, and at others re· sembles a rod, terminated in the males by two lamellar appendages varying in form according to the species(2); and, finally, short legs curved forwards. The under part of the second annulus of the abdomen contains the sexual organs of the males, and as those of the females are situated on the last ring, the coition of these Insects is effected in a different manner from that of othe1·s. The male, first hovering ovet· his fe· male, sf'izes her by the neck with the hooks that terminate the pos· terior extremity of his abdomen, and flits away with her. After a shorter or longer period, the latter, yielding to his desires, curves her abdomen downwards, and approximates its extremity to the genitals of the male whose body is then bent into the form of a buckle. This junction frequently occurs in the air and sometimes on the bodies where they alight. To lay her eggs the female places herself on some aquatic plant that is raised but little above the water, into which she plunges the posterior extremity of her abdomen. The larvre and the chrysalides inhabit the water until the period (1) For their structure, see Cuv., Mem. de la Soc. d'Hist. Nat., de Par., 4to, P· 41. (2) MM. Van der Linden and Toussaint Charpentier have made a particullll' study of these appendages. The latter has carefully figured all these varieties in his llorm Eniotnologicm. The genus Petalura, Leach, Zool. Miscel., being essentially established on ch;lracters drawn from these appendages, appears to me to be ina~missible, and for the simple reason, that if this ground of division be o~ce recetved, we shall have to establish almost as many genera as there are spectes. NE'UROPTERA. 59 of their ultim~te. metamorphosis, ancl, with the exception of wings, are tolerably simtlar to the perfect Insect. Their head, however, on which the simple eyes are not perceptible, is remarkable for the singular form of the piece whic~ replaces the lower lip. ·It is .a kind of mask that covers the mandibles, maxillre, and almost the whole undet• part of the head. It is composed, 1, of a principal triangular piece that is sometimes arched and sometimes flat, called by Reau· mur the mentonniere ( chin·cloth ), articulated by a hinge with a pe· dicle Qr sort of handle annexed to the head; 2, of two other pieces inserted at the superior and lateral angles of the former, movable at base, transversal, and either in the form of wide and dentated lamin~ resembling shutters in their motion and the manner in which they close the mouth, or in the form of hooks or little claws. To this part of the mask where the mentonniere is articulated with its pedicle, or the knee, and which appears to terminate it inferiorly when the mask is flexed upon itself, Reaumur applies the name of mentum. The insect unfolds or extends it with great promptitude, and seizes its pt·ey with the pincers of its superior portion. The posterior extremity of the abdomen sometimes presents five foliaceous and unequal appendages, which the animal can separate and approximate, in which case they form a sort of pyramidal tail; sometimes we observe the three elongated and pilose lamince or a sort of fins. We. see. these Insects unfold them every moment, open their rectum, fill1t wtth water, then close it, and shortly afterwards ejaculate that water mixed with large bubbles of air, a game that appears to facilitate theil· motions. The interior of the rectum(l) presents to the naked eye twelve longitudinal ranges of little black spots, upproxi· mate? by pairs, r.esembling the pinnatrd leaves of botanists. By the atd of the microscope we discern that each of these spots is composed of little conical tubes, organized like t1·achere, and f1·om which originate small branches that proceed to six large trunks of the principal trachere that traverse the whole length of the body. Having attained the pel'iod of their ultimate metamorphosis, the nymphs iss~e from the water, climb along tho stems of plants, fix there, and d1vest themselves of their skin. M. Poe, who has paid particular attention to the Insects of the island of c.u ba, informs me that at a certain season of the year the tlorthe~·n wmds sw~ep an innume1·able host of a species of this genus -spec1mens of which he had the kindness to send me-into Havana or its environs. (1) Cuv., Mem. de Ia. Soc. <l'Hist. Nat., 4to, p. 48. |