990 



INSECTS AND ARACHNIDA 



and it also forms the 'tongue' of the bee and its allies (fig. 73ft). 

 The ligula of the common fly presents a curious modification of the 

 ordinary trachea! structure, the purpose of which is not apparent ; 

 for instead of its tracheae being kept pervious, after the usual 

 fashion, by the winding of a continuous spiral fibre through their 

 interior, the fibre is broken into rings, and these rings do not sur- 

 round the whole tube, but are terminated by a set of arches that pass 

 from one to another (fig. 739, B). 1 In the Diptera, or two-winged 

 flies generally, the labrum, maxilla?, mandibles, and the internal 

 tongue (where it exists) are converted into delicate lancet-shaped 

 organs termed setce, which, when closed together, are received into 



a hollow on the upper side of the 

 labium (fig. 739), but which are 

 capable of being used to make 

 punctures in the skin of animals or 

 the epidermis of plants, whence 

 the juices may be drawn forth by 

 the proboscis. Frequently, how- 

 ever, two or more of these organs 

 may be wanting, so that their 

 number is reduced from six to 

 four, three, or two. In the 

 Hymenoptera (bee and wasp tribe) 

 the labrum and the mandibles 

 (fig. 738, 6) much resemble those 

 of mandibulate insects, and arc 

 used for corresponding purposes ; 

 the maxilla? (c) are greatly elon- 

 gated, and form, when closed, a 

 tubular sheath for the ligula, ox 

 tongue,' through which the 

 honey is drawn up; the labial 

 palpi ('7) also are greatly de- 



Fm. 788. Parts of the mouth of Ajtis 

 iHt'U/Jicd (honey-bee) : a, mentuni ; 5, 

 mandibles ; r, maxilla.- ; <1, labial palpi ; 

 e, ligula, or prolonged labium, com- 

 monly termed the ' tongue.' 



drawn up 

 also are 



veloped. and fold together, like 

 the maxillie, so as to form an 

 inner sheath for the ' tongue ; ' 

 while the ' ligula ' itself (e) is a 



long tapering muscular organ, marked by an immense number of 

 .short annular divisions, and densely covered over its own length 

 with long hairs. It is not tubular, as some have stated, but is 

 solid : when actively employed in taking food it is extended to a 



reader is referred to Mr. Suffolk's memoir, 'On the i'roboseis of the Blow-rly,' in 

 Mniithhi MiiTdM-. linini. i. p. 331, and to Mr. Lowne's treat ise on Tl/e Anatomy 

 <t ml Physiology <//'// Jiln/r-fl//. 



' . \rcordlng to Dr. Anthony (Monthly Mii't'iixi'ii/iirnl Junrii. vol. xi. p. 24'2), these 



P eudo tracheae' aiv Mictorial organs, which can take in liquid alike at their ex- 



tremities and through the whole length of the fissure caused by the interruption of 



the rings, tin- edge-, of this lissnre being formed by the alternating series of 'ear-like 



appendages ' ronnreted with the terminal ' arches,' the closing together of which 



converts the pseudo-tracheae into a. complete tube. Dr. Anthony considers each of 



I In e ear Like appendages to be a minute sucker, 'either for the ail I lesion of the fleshy 



in-, or for tin- imbibition of fluids, or perhaps for both purposes.' The point is 



\\ell worthy of further investigation. 



