990 



INSECTS AND AEACHNIDA 



and it also forms the 'tongue' of the bee and its allies (fig. 738). 

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

 ordinary tracheal structure, the purpose of which is not apparent ; 

 for instead of its trachea? 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, b) much resemble those 

 of mandibulate insects, and are 

 used for corresponding purposes ; 

 the maxilla? (c) are greatly elon- 

 gated, and form, when closed, a 

 tubular sheath for the ligula j or 

 ' tongue,' through which the 



FIG. 738. Parts of the mouth of Api 



honey is drawn up ; the labial 

 palpi (d) also are greatly de- 

 \elopecl, ^d fold together, like 



ligula, or prolonged labium, com- the maxilla?, so as to form an 

 monly termed the ' tongue.' 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 Proboscis of the Blow-fly,' in 

 Monthly Microsc. Journ. i. p. 331, and to Mr. Lowne's treatise on The Anatomy 

 and Physiology of the Blow-fly. 



1 According to Dr. Anthony (Monthly Microscopical Journ. vol. xi. p. 242), these 

 ' pseudo-tracheae ' are suctorial 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, the edges of this fissure being formed by the alternating series of ' ear-like 

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

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

 these ear-like appendages to be a minute sucker, ' either for the adhesion of the fleshy 

 tongue, or for the imbibition of fluids, or perhaps for both purposes.' The point is 

 well worthy of further investigation. 



