INSECTA. 



609 



its outer surface, but concave on its inner; so that when 

 the two are approximated, they form a tube by their union, 

 through which fluids may be drawn into the mouth. The 

 inner or concave surface, which forms the tube, is lined 

 with a very smooth membrane, and extends throughout 

 the whole length of the organ ; but that each maxilla is 

 hollow in its interior, forming a tube ' in itself/ as is 

 generally described, is a mistake; which has doubtless 

 arisen from the existence of large tracheae, or breathing- 

 tubes, in the interior of each portion of the proboscis. In 

 some species, the extremity of each maxilla is studded 

 externally with a great number of minute papilla?, or 

 fringes — as in the Vanessa atalanta — in which they are 

 little elongated barrel-shaped bodies, terminated by smaller 

 papillae at their extremities." Mr. Newport supposes that 

 the way in which the insect is enabled to pump up the 

 fluid nourishment into its mouth is this : " On alighting on 

 a flower, the insect makes a powerful expiratory effort, by 

 which the air is expelled from the interior air-tubes, and 

 from those with which they are connected in the head and 

 body ; and at the moment of applying its proboscis to the 

 food, it makes an inspiratory effort, by which the central 

 canal in the proboscis is dilated, and the food ascends it at 

 the same instant to supply the vacuum produced; and 

 thus it passes into the mouth and stomach : the constant 

 ascent of the fluid being assisted by the action of the 

 muscles of the proboscis, which continues during the whole 

 time that the insect is feeding. By this combined agency 

 of the acts of respiration and the muscles of the proboscis, 

 we are also enabled to understand the manner in which 

 the Humming-bird sphynx extracts in an instant the honey 

 from a flower while hovering over it, without alighting; 

 and which it certainly would be unable to do, were the 

 ascent of the fluid entirely dependent upon the action of 

 the muscles of the organ." 1 



The wings of Moths and Butterflies are covered with 

 scales or feathers, carefully overlapping each other, as tiles 

 are made to cover the tops of houses. The iridescent variety 

 of colouring on their wings arises from a peculiar wavy 

 arrangement of the scales. Figs. 272 and 273 are magni- 



(1) Cyclop. Anat. Physiol., article "Insecta." 

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