STRUCTURE OF THE ORTHOPTERA. 



119 



HEAD AND MOUTH ORGANS OF COCKROACH. 

 (After Griffith and Henfrey. ) 



1 



and when present they are more frequently three than two in number. In the antenna) we find 

 the same difference as in the Rhynchota, these organs being either long and thin, generally thread- 

 like or bristle-shaped, and composed of numerous joints, or small organs, consisting of two or 

 three basal joints and a bristle, which, however, may be jointed. 



In the structure of the thorax there is considerable difference, although the three seg- 

 ments are generally separate. The prothorax is frequently of large size, forming the principal 

 part of the thorax as seen from above, but sometimes it is much reduced, representing a sort of 

 ring-like neck ; the meso- and nietathorax are well developed, 

 and in the great majority of the species are furnished with a 

 wings. These latter organs are entirely wanting in the parasitic 

 forms that we refer to the order, and in a few members of other 

 groups ; but in general we find four wings, which, however, difier 

 greatly in texture. Thus in one large section of the order 

 the fore wings are of a leathery or horny consistence, generally 

 forming protective coverings (tegmina) for the hind wings, 

 which are more membranous, and in which the veins radiate 

 from a central point to the margin, so that in repose the wings 

 fold together after the manner of a fan ; whilst in another 

 great division both pairs of wings are membranous, and serve 

 as organs of flight, and the veining of both pairs is more or less 

 alike. The legs are very various in their character. 



Like the labium, the abdomen shows in its structure 

 traces of approximation to the ideal type of insects, inasmuch 

 as in many cases this part of the body shows the whole number A 

 of eleven segments (see Fig. 2, p. 282, Vol. V.). The extremity 

 of the abdomen is often furnished with appendages of various 



kinds, sometimes with long and slender bristles, sometimes with stouter jointed tails (cerci), and 

 occasionally with horny processes, which may take on the form of forceps. In some forms the 

 abdomen of the female is furnished with an ovipositor, which represents the ventral plate of the 

 ninth abdominal segment, the genital and anal orifices being here separated, and placed, the former 

 in the ninth, the latter in the eleventh segment. 



Of the internal structure of the Orthoptera in general we can say but little. The intestinal canal 

 (see figure on p. 120) is rarely much longer than the body. The ossophagus is followed by a gizzard, or 

 proventriculus, chiefly in those forms which live upon an animal or mixed diet, and the salivaiy glands 

 are more highly developed in the same species. In most Orthoptera the Malpighian vessels are short 

 and numerous. The ventral nervous chain follows the generalised type of the segmentation o 

 the abdomen, the abdominal ganglia, as well as the thoracic, being distinct, and united only by 

 commissures, except at the extremity of the chain, where two or more of the abdominal ganglia 

 are united into a mass. A remarkable character of this ventral chain is that it is so long that 

 if stretched out it would extend beyond the abdomen, and it consequently forms one or more curves 

 in its course through the body. The tracheae are frequently dilated into air- vesicles in those forms 

 which possess much power of flight. 



Of the preparatory stages of these insects little need be said. The parasitic and apterous 

 forms appear to undergo no changes of consequence, and the larvae of a great number of the higher 

 types are almost exactly like their parents, except for their smaller size and the absence of wings. 

 In some cases, however, including nearly all the forms which pass their preparatory stages in the 

 water, there is rather more difference between the larva and the perfect insect, although the 

 former is still active in all its stages. In all the development is quite gradual ; the young larvae 

 are destitute of any traces of wings, which, however, soon make their appearance beneath the 

 skin behind the prothorax, and go on increasing in size with each moult, until the final change 

 takes place. During this process the number of joints in the antennae, and the number of facets 

 in the compound eyes, usually increase with each change of skin. The larvae seek the same diet 

 as the perfect insects, and are generally exceedingly voracious. 



