3132 THE JOINTED ANIMALS 



or habit. In past epochs of the earth's history Orthoptera were well represented, 

 their remains being found in rocks of various ages extending back to Paleozoic 

 times. The oldest reputed insect is known by the impression of an orthopterous 

 wing (Palceoblattina} , from the Silurian sandstone of Calvados in France. There 

 is some doubt as to which group of the order the insect belonged, and even as to 

 whether the impression owed its origin to an insect at all. However this may be, 

 traces of undoubted Orthoptera, as well as of Neuroptera, are met with in rocks of 

 Devonian and Carboniferous ages. The Orthoptera of the latter period included 

 numerous cockroaches (Blattidce), together with stick insects, ephemerids, and 

 dragon flies, some of which greatly exceed in size any existing form. One of the 

 dragon flies (Meganeura monyi) , was thirteen inches in the length of its body, and 

 each of its wings was quite a foot long. 



The Pseudoneuroptera are distinguished from the Neuroptera by the absence 

 of a pupal stage. While agreeing in this respect with the typical Orthoptera, these 

 insects differ by certain characteristics not generally considered of the first impor- 

 tance. Both pairs of wings in this group are thin and membranous, resembling one 

 another in structure, and the hind-wings do not fold up; whereas in the true Or- 

 thoptera the fore- wings are usually thicker and harder than the hind-wings, and the 

 latter are capable of being folded like a fan. 



The first group is that of the dragon flies (Odonata), the general 

 appearance of which is too well known to need description. All have 

 a large head, the sides of which are covered almost entirely by the two big, glassy- 

 looking, compound eyes, while on its crown are two or three small simple ocelli. 

 Each of the short and bristle-like antennae has a stouter basal portion by which it 

 is inserted on the forehead. The mouth faces downward, and has a large semicir- 

 cular lip (labrum) in front; the jaws being strong, horny, and well provided with 

 teeth. The maxillae are without palpi, but their narrow and palp : like outer lobe is 

 often regarded as the real palp. Succeeding the jaws behind is the lower lip 

 (labium), which at its free end is usually slightly cleft in the middle, while its palpi 

 take the form of two dilated and often two- jointed lateral lobes; these lobes some- 

 times overlapping one another in front to hide the free end of the lip. The thick 

 and cylindrical thorax is followed by a long slender abdomen, which usually carries 

 at the end two leaf-like or pincer-like appendages. When looked at from the side, 

 the two hinder segments of the thorax appear oblique, with the wings set rather far 

 back above, and the legs pushed forward below. The wings are long, transparent, and 

 traversed by a rich network of veins. The legs are often spiny, and their tarsi 

 are always three jointed. The position of the accessory organs of the male on the 

 under side of the second abdominal ring is a feature distinguishing dragon flies from 

 other insects. 



The female dragon fly deposits her eggs in such a position that the larvae, when 

 hatched, find themselves either in their natural element, the water, or very close to 

 it. In some species the female, accompanied by the male, goes under the water to 

 lay her eggs; others drop them into the water; while in many species the female 

 makes incisions in some aquatic plant and there deposits her eggs. The larvae are 

 even more fiercely carnivorous than the adult, and are distinguished from all other 



