INSECTA. 



873 



the mouth is bounded by a membranaceous 

 labium, while at its anterior part it is furnished 

 with a proboscidal lip (fig. 358, B c), divided 

 into four very minute palpiform organs. There 

 are also two processes situated one on each 

 side of the mouth in the second segment. At 

 the base of the fourth segment are the two pro- 

 jecting orange-coloured organs of a semicircular 

 form, divided into what appear like single 

 pedunculated eyes, but which are in reality 

 external branchiae, and correspond to the spira- 

 cles of the pro-thorax of the perfect insect (A). 

 In the (Estrus ovis (fg. 360) the two sides of 



length, and the parts of which they are 

 composed are readily distinguished. These 



Head of larva of (Estrus ovis. 



2, 3, 4, segment ; a, optic nerve ; b, epicranium ; c, 

 labium ; d, mandibles ; e, maxillce. 



the fissure that forms the anterior part of the 

 mouth are developed into very distinct organs 

 of vision (A), in which may be traced the nerves 

 of two separate but nearly approximated eyes. 

 The existence of distinct eyes in this larva is 

 the more remarkable, from the circumstance that 

 the larva resides in the frontal sinus of the skull 

 of the sheep, where we sought for, and found 

 the identical specimens upon which our obser- 

 vations have been made. 



Organs of locomotion. We stated above that 

 the true organs of locomotion are six in num- 

 ber, both in the larva and perfect state, and 

 that they are always attached to the second, 

 third, and fourth segments of the body. They 

 are distinguished from the false, or abdominal 

 legs by their possessing distinct articulations 

 or joints, by the strength and hardness of their 

 texture, and by their general pointed form. In 

 Coleopterous larvae they are of considerable 



Fig. 362. 



Fig. 361. 



Fig. 361. Thoracic leg of larva of Cossus ligniperda 

 (Lyonet). 



a, Coxa ; b, femur ; c, tibia ; d, tarsus ;/, ungui*. 

 Fig. 362. Abdominal leg. 



are (Jigs. 361, 364 ***), as in the perfect 

 insect, the claw (/), the tarsus (d), the tibia 

 (c), the femur (6), and coxa, or hip (a). In all 

 terrestrial larvae the legs are attached to the 

 inferior parts of the segments; but in one 

 remarkable genus of water-beetles the great 

 Hydrous piceus, they were supposed by Frisch 

 to be attached so much nearer to the dorsal 

 than the sternal surface as to have the appear- 

 ance of being actually placed on the back. But 

 this is erroneous, the mistake having arisen 

 from the peculiar formation of the head, which 

 is flat on its upper, but convex on its under sur- 

 face. The whole of these thoracic legs, in all 

 larvae which possess them, are nearly equally 

 developed, and do not present any marked 

 difference of form or size, as is often sub- 

 sequently found in the perfect insects. In the 

 larvae of Lepidoptera they are exceedingly 

 short and pointed, and in many Hymenoptera 

 and Diptera are entirely absent. The false or 

 abdominal legs are totally different in appear- 

 ance and structure from the true or thoracic ones. 

 Although varying in number in different species, 

 they are universally present in the Lepidoptera 

 (Jig. 364, ftt) and in many Hymenoptera and 

 Diptera. In some instances, as in many of 

 the Geometrida, there is only a single pair at 

 the anal extremity of the body ; while in others, 

 as in some of the Tenthredinidte, there are as 

 many as eight pairs. In every instance they 

 are soft and membranaceous, without distinct 

 joints or articulations. In some of the Lepi- 

 doptera their structure is exceedingly curious, 

 and has been beautifully illustrated by Lyonet 

 (Jig. 362), in his anatomy of the larva of 

 Cossus ligniperda. In that insect their shape 

 resembles an inverted cone, with its apex trun- 

 cated to form a flat sole, or foot, upon which 

 the caterpillar walks. The sole in its middle 

 can be rendered concave at the will of the 

 animal, while around its margin are several 

 rows of minute hooks, directed outwards, and 

 when the sole of the foot is pressed firmly upon 



