INSECTA. 



901 



been described as being hollow in its interior, 

 or forming " in itself a tube,"* which appears 

 to have arisen from the circumstance of there 

 existing in each, one or more large tracheal 

 vessels, (Jig. 378, 6, e,) connected with the 

 tracheae of the head, and which are divided, as 

 they approach the extremity of the organ, into a 

 great number of minute ramifications, but which 

 have no communication with the external sur- 

 face, their distribution being precisely similar to 

 that of the trachese in other parts of the body. 

 The maxilla is composed of elementary parts, 

 as in the preceding Orders, but they are not 

 easily distinguished. The long extensile por- 

 tion is the proper lacinia, which is constricted 

 at its base, immediately beyond which is situ- 

 ated, in Sphinx ligustri, a minute three-jointed 

 hairy palpus (h). Mr. Newman could not de- 

 tect this maxillary palpus in Sphinx,f and hence 

 concluded that it was obsolete in this family. 

 It is indeed exceedingly minute and easily 

 overlooked, but is distinctly three-jointed, and 

 densely covered with long hairs. The structure 

 of the maxillae in different genera and species 

 is particularly interesting, and their length is 

 exceedingly various. Thus in the Sp/ungid*, 

 in Smerinthus ocellatus, which takes no food, 

 they scarcely exceed one-eighth of an inch, 

 while in Sphinx ligustri, which continues ho- 

 vering on the wing while extracting the sweets 

 from a flower, they are nearly two inches in 

 length, and this is also the case in the hum- 

 ming-bird moth, Macroglossa stellatarum. 

 In the butterflies, and in many of the Noc- 

 titidz, they are often about equal to the length 

 of the body. The inner or concave surface 

 which forms the tube is lined with a very 

 smooth membrane, and extends along the an- 

 terior margin throughout the whole length of 

 the organ, as in the transverse section, (fig. 

 378, 6, 6.) At its commencement at the apex 

 it occupies nearly the whole _ breadth of the 

 organ, and is rather smaller than at its termi- 

 nation near the mouth, where the concavity or 

 groove does not occupy more than about one- 

 third of the breadth. In some species the ex- 

 tremity of each maxilla is furnished along its 

 anterior and lateral margin with a great number 

 of minute papillae, but in others these parts are 

 entirely absent. They are extensively deve- 

 loped in some of the butterflies, as in Vanessa 

 atalanta, (fg. 378, 1, 2, c,) in which they 

 are little elongated barrel-shaped bodies, (4, c,) 

 terminated by three smaller papillae, arranged 

 around their anterior extremity, with a fourth 

 one a little larger than the others placed in 

 their centre. These papillae are arranged in 

 two rows along the lateral and anterior surface 

 of each maxilla, near its extremity, for about 

 one-sixth part of its whole length, as at 1, and 

 5, c, d. There are seventy-four in each max- 

 illa, or half of the proboscis. To judge from 

 their structure, and from the circumstance that 

 they are always plunged deeply into any fluid 

 when the insect is taking food, they may pro- 



Fig. 378. 



Parts of the maxillae or proboscis of Vanessa atalanta. 



\, external surface of the apex with the double 

 row of papillae ; 2, internal or concave surface ; a, 

 transverse muscles; 6, tube; c, papillae; d, hooks 

 which join the maxillae; 3, one of the hooks ; 4, 

 one of the papillae ; 5, section of the tip of the 

 maxillae, showing the position of the papillae on each 

 side of the tube ; 6, section of maxillae near their 

 base, showing the position of the tube, 6; the large 

 trachea, e, and the smaller one and nerve, /. 



bably be regarded as organs of taste. They are 

 largely developed in this genus of insects, but 

 in Pontia, the common white butterflies, and 

 in Sphinx ligustri they are scarcely perceptible. 

 There are also some curious appendages ar- 

 ranged along the inner anterior margin of each 

 maxilla, in the shape of minute hooks, which, 

 when the proboscis is extended, serve to unite 

 the two halves together. They were first no- 

 ticed by Reaumur,* and subsequently by Mr. 

 Kirby.t In many insects, as in Sphinx and 

 Pontia, they have more the appearance of 

 cilia, like the barbs of a feather, than of hooks, 

 but in Vanessa they are falcated, and furnished 

 with an additional tooth (3, d} a little beyond the 

 apex. They are so exceedingly minute, and ar- 

 ranged so closely together, that their true form 

 is with difficulty distinguished. They lock 

 across each other like the teeth in the jaws of 

 some fishes, and we are inclined to believe that 

 the points of the hooks in one-half of the pro- 

 boscis are inserted, when the organ is extended, 

 into little depressions between the teeth of the 

 opposite side, so that they form the anterior 

 surface of the canal, but of this we are not con- 



* Newman on the Head of Insects, p. 28. 

 t Op. cit. p. 28. 



Memoires, &c. torn. i. p. 125. 

 Introduction, vol. i. p. 394. 



