146 NATURAL HISTORY. 



mouth. In seizing a prey it is darted out towards the victim, which is firmly grasped by the apical 

 forceps, and then easily conveyed within reach of the other organs of the mouth. 



Besides the difference of form, these larvae also present important differences in their respiratory 

 apparatus. In the Agrionides the larvae are always provided with external branchial organs appended 

 to the extremity of the abdomen, sometimes alone, sometimes in conjunction with an internal 

 breathing apparatus similar to that prevailing in the other two groups, which consists of a peculiar 

 arrangement and ramification of tracheae in the walls of the rectum or terminal portion of the 

 intestine. The water is drawn into and expelled from this by the action of special muscles, and the 

 expulsion is so forcible that the creatures are slowly moved through the water by its recoil. The 

 insects are active and voracious throughout their preparatory stages, in the last of which they show 

 large wing-cases behind the thorax. When full grown they crawl up the stems of some aquatic 

 plant into the open air, and after resting there for a longer or shorter time, the skin splits along the 

 thoracic region, and the perfect insect by degrees struggles out of its investment. The wings, at first, 

 have not attained their full development, but this is soon reached, and the Dragon Fly starts off 

 to continue in the air the same scene of rapine that has characterised its subaqueous existence. 



SUB-ORDER III. PHYSOPODA. 



The Physopoda are a curious group of insects, the true position of which has been always 

 doubtful. Some writers place them with the Orthoptera, others with the Rhynchota, and others again 

 in a separate order, side by side with one or other of those just mentioned. We have preferred here 

 to follow Burmeister and those entomologists who have adopted his view of the matter. 



These insects have a narrow flattened body, and two pairs of narrow wings, which sho\v 

 few or no veins, but have their margins fringed with longish hairs, whence the name of 

 Thysanoptera (or "fringed wings") was applied to the group by the late Mr. Haliday. In repose, 

 these wings lie flat over one another iipon the back of the abdomen, leaving the margins of the latter 

 exposed. The head is of a somewhat cylindrica* form, and bears a pair of large eyes, a pair of 



antennae consisting of eight or- 

 nine joints, and three ocelli placed; 

 between the eyes. The w^ngs and, 

 ocelli are deficient in so,np,e species. 

 The mouth is bent back; tpwards. 

 the breast, and pointed-, so as to> 

 remind one of the character of the 

 rostrum in the Homoptera, and 



LARVA (A) AMD IMAGO (B) OF THRIPS CEREALIUM. Stiil more in tllG WotonectO!, but 



. .. ' its structure is very different. 



Thus the mouth is closed in front by a pointed labrum, behind which is a pair of bristle-like, 

 mandibles more or less dilated at the base. Within these again are found two simple maxillee, bearing 

 palpi of two or three joints; and the whole apparatus is completed by a membranous labium, 

 pointed in front, and furnished with short two-jointed palpi. The legs are of moderate length, or 

 short, and have tarsi of two joints, the second of which bears no claws, but terminates in a bladder- 

 like disc, by means of which the insects adhere to the objects upon which they walk, Hence arises 

 the name of Physopoda, and the action of these little suckers causes the insects, to, produce a very 

 uncomfortable tickling sensation when they run upon the skin of people's faces. 



The insects of this group are all small. The ordinary run of species are about one4welth of an. 

 inch long, many less, and those of an eighth of an inch may be looked upon as large. From this 

 point of view the species of Jdolothrips, which inhabit Australia, are gigantic, measuring from a 

 quarter to a third of an inch in lengch. The Physopoda are no doubt abundant in all parts of 

 the world, but comparatively few extra-European species have been recorded. In Europe, however, 

 they are numerous, and may be found throughout the summer upon the leaves and flowers of plants, 

 especially the latter, where they often look like so many black streaks scattered over the bright 

 petals. Many of them, however, are not black, and some seem to copy the colours of their favourite 

 flowers. The larvae, in all stages, are fcund in the same situations as the perfect insects, which they 



