no 



HARDWICKE'S SCIENCE-GOSSIF. 



third, the flexible under-surface of the thorax is 

 inclined, so as to form a nearly vertical step. In the 

 two hinder of these steps a chitinous prop is fixed ; 

 ■each is Y-shaped, with long, curved arms for 

 muscular attachment, and a central notch, which 

 •supports the nerve-cord. A third piece of similar 

 nature (the antefurca), which is well developed in 

 ■some insects, -f.^., in ants, is apparently wanting in 

 the cockroach. 



Three pairs of legs are attached to the thoracic 

 ■segments ; they regularly increase in size from the 

 first to the third, but hardly differ except in size ; 

 the peculiar modifications which affect the fore pair 

 in predatory and burrowing Orthoptera {Mantis, 

 Gryllotalpa), and the third pair in leaping Orthoptera 

 {Acridiiiiii), being absent in the cursorial Blattina. 

 Each leg is divided into the five segments usual in 

 insects (see fig. 65), and there are also basal pieces, 

 which apparently represent a sixth joint. 



The legs of the cockroach, when bearing the 

 weight of the body, are bent variously to such an 

 ■extent that the abdomen rests lightly on the ground. 

 In locomotion three of the six legs move nearly 

 simultaneously ; these are a fore and hind limb of 

 ■one side, and the opposite middle leg. The legs 

 differ in their action ; the fore-leg may be compared 

 to a grappling-iron ; it is extended, seizes the ground 

 with its claws, and is then flexed so as to draw the 

 body forwards ; the hind leg is used for shoving ; 

 and the middle leg serves to support the body while 

 the fore and hind limb of the opposite side are pulling 

 and pushing. 



Cockroaches of both sexes are provided with wings, 

 which, however, are only functional in the male. 

 The wing-cases (or anterior pair of wings) of the 

 male are carried by the second thoracic segment. 

 As in most Orthoptera genuina, they are denser than 

 the hind wings, and protect them when at rest. 

 They reach to the fifth segment of the abdomen, and 

 the left wing-case overlaps the right. Branching 

 veins or nervures form a characteristic pattern upon the 

 surface (see fig. 66), and it is largely by means of this 

 pattern that many of the fossil species are identi- 

 fied and distinguished. The true or posterior wings 

 are attached to the metathorax. They are mem- 

 branous and flexible, but the fore-edge is stiffened, 

 like that of the wing-cases, by additional chitinous 

 ■deposit. When extended, each wing forms an ir- 

 regular quadrant of a circle ; when at rest, the radia- 

 ting furrows of the hinder part close up fan-wise, and 

 the inner half is folded beneath the outer. The wing 

 reaches back as far as the hinder end of the fourth 

 abdominal segment. The wing-cases of the female 

 ^re small, and though movable, seem never to be 

 •voluntarily extended ; each covers about one-third of 

 the width of the mesonotum, and extends backwards 

 •to the middle of the metanotum. A reticulated 

 pattern on the outer fourth of the metanotum plainly 

 srepresents the hind wing ; it is probably rather a 



degeneration or survival than an anticipation of an 

 organ tending towards useful completeness. 



The rudimentary wing of the female cockroach 

 illustrates the homology of the wings of insects with 

 the free edges of thoracic terga, and the same con- 

 clusion is enforced by the study of the development of 

 the more complete wings and wing-cases of the male. 

 The hinder edges of the terga become produced at 

 the later moults preceding the completely winged 

 stage, and may even assume something of the shape 

 and pattern of true wings ; it is not, however, true, 

 though more than once stated, that winged pupse are 

 common. Adults with imperfectly developed wings 

 have been mistaken for such, though the sexual 

 characters of the hinder part of the abdomen, which 

 are only present in the last stage of growth, distin- 

 guish such forms from true' pupce. 



Tlie structure of the wing testifies to its origin as a 

 fold of the chitinous integument. It is a double 

 lamina, which often encloses a visible space at its 

 base. The nervures, with their vessels and tracheal 

 tubes, lie between the two layers, which, except at 

 the base, are in close contact. Oken termed the 

 wings of an insect "aerial gills," and this rather 

 fanciful designation is in some degree justified by 

 their resemblance to the tracheal gills of such aquatic 

 larvae as are found in Ephemerida;, Perlidse, Phrya- 

 nidse, &c. In the larva of Chlocon {Ephemera) 

 dimidiatuin, for example, the second thoracic segment 

 carries a pair of large expansions, which ultimately 

 are replaced by organs of aerial flight. The third 

 thoracic segment is provided with small appendages, 

 resembling wings in position and texture, but of no 

 importance for locomotion ; to these succeed similarly 

 placed respiratory leaflets, the tracheal gills of the 

 abdominal segments, which by their vigorous flapping 

 movements bring a rush of water against their 

 membranous and tracheated surfaces. It would be 

 going too far to say that the primitive insect-wing 

 was specially adajDted to respiration or locomotion 

 in water, but the aerial wing may certainly closely 

 resemble, both in structure and development, organs 

 converted to these uses.* 



The wings of the cockroach have little functional 

 activity. The male will sometimes fly to fresh 

 quarters, as from one house to anothei\ At times of 

 sexual excitement it raises the wings, but does not 

 rise in the air. Even in extremity it will not fly to 

 escape from danger. Readers will recollect the 

 Amblyrhynchus, a maritime lizard of the Galapagos, 

 described by Darwin, f Though an excellent swimmer 

 and diver, it will not enter the water when frightened. 

 Darwin suggests that the reptile has no enemy on 



* Wing-like expansions, serviceable either for locomotion, 

 aquatic respiration, or aerial respiration, can apparently be de- 

 veloped or suppressed as required, not only in insects, but in 

 many other animals. It appears from Palmen's researches that 

 all tracheal gills are not homodynanious or equivalent. Some 

 are dorsal in position, others ventral ; some are folds of integu- 

 ment, others moditied appendages. 



t " Naturalist's Voyage," chap. xvii. 



