TONGUE AND MOUTH PARTS. 93 



a beautiful gradation of form, from row to row, are 

 short and triangular in shape near the base of the 

 organ, long and spiny about the middle, smaller 

 and more flexible near the apex, while amongst them 

 are found hairs with a bulbous structure, provided with 

 a nerve which constitutes them touch organs, or true 

 tactile hairs (tk, I, Plate III.). The high elasticity 

 of the ligula, depending upon the structure of a rod 

 running through its centre, allows it to be used as a 

 lapping tongue when any considerable quantities of 

 syrupy food are at command. As it then sweeps 

 backwards and forwards, the front side turned down,, 

 the gathering hairs (gh, Plate III.) get loaded, while 

 the labial palpi and maxillae are so placed round it 

 as to form a perfectly airtight tube. C, D, E, 

 Plate III., show the palpi with the hairs crossed 

 behind, while the hyaline plates {hp, C) of the two 

 maxillae lie over one another. Each maxilla is 

 beautifully furnished with a line of hairs (h) in front 

 of it, and a groove at its back ; both of these act as 

 mechanical stops, and accurately adjust the position 

 of the two maxillae, preventing them, as they are 

 drawn together by their proper muscles, from ap- 

 proaching too nearly whichever plate may happen to 

 take the front position. But although the tube so 

 made up is airtight, it cannot act as a suction pipe, 

 because it is open above, as may be seen by 

 reference to Plate II. But now the front extension 

 of the epipharynx (g) closes down to the maxillae, 

 fitting exactly into the space they leave uncovered, 

 and thus the tube is completed from their termination 

 to the oesophagus. 



