52 The Larva of Chironomus 



there is at least tlie resemblance implied in a thick 

 muscular wall and a dense cuticle. Of course the gizzard 

 of the bird is part of the vertebrate stomach, while that 

 of the insect is part of the arthropod oeso])hagus. If we 

 will employ no vertebrate terms except strictly in the 

 vertebrate sense, we shall be forced to invent unfamiliar 

 and cumbrous expressions of our own. Plateau's appareil 

 valvulalre. which he proposes to substitute for gizzard, 

 is liable to be confounded with the oesophageal valve 

 next to be mentioned. The lower end of the oesophagus 

 of insects commonly protrudes into the mid-gut, and 

 is then reflected, forming a circular valve, the cardiac 

 or oesophageal valve of authors. The latter designation 

 is preferable. 



For the mid-gut or mesenteron in the coinpletely 

 developed insect, stomach is a convenient term. Plateau 

 points out that the so-called stomach of insects is absorbent, 

 l3ut not secretory. It is not, however, clear that such 

 plijrsiological distinctions, even if well founded ', need 

 affect our nomenclature. The fore part of the stomach 

 sometimes forms a distinct cardiac charnber, and into 

 this, if present, the glandular caeca, which often project 

 from the stomach, usuallj^, but not always, open. 



The name intestine may be applied to all parts deve- 

 loped from the hind-gut. The intestine is often divisible 

 into a fore section (small intestine), a middle section 

 [colon), and a terminal section [recttmi). The walls of 

 the rectum are often longitudinally folded. 



Mouth. The mouth lies between the labrum in front and the 



labium behind ; on either side are the mandibles and 

 the greatly reduced maxillae (fig. 19}. The labrum 

 has the form of a flap ; its free border is bent back- 

 wards when at rest, and the surface which faces the 

 mouth (epiphari/nx of some authors) is armed with many 

 teeth, ras23ers, and setae, whose disposition can be seen 

 in fig. 16. Some of these are probably sensory, others 

 defensive, and others again masticatory or prehensile. 

 The labrum is muscular and mobile ; it is often employed 

 to assist the mandibles in rasping the food, grinding it 



' See Secretion of the stomacli, p. 57. 



