The Jazvs 29 



other, but rather to the strongly toothed snhmentnm. 

 On the inner side of each mandible is a bunch of setae, 

 which help to close-in the mouth. The first pair of 

 maxillae are not so easy to make out, for they are reduced 

 to stumps, which are concealed from view when the head 

 is at rest. There is a rudimentary setose prominence 

 internally;, which in some species bears a row of tooth- 

 lihe projections, and a minute palp on the outer side. 

 The maxillae of the second pair, which often unite to 

 form a single organ, the labium, can only be understood 

 by comparison with other insects. In the Chironomus- 

 larva they have lost so many of the original parts that at 

 first sight they seem to consist of a single comb-like plate, 

 whose teeth point forwards, and are opposed to the man- 

 dibles, helping them to grasp or divide the food. On 

 close examination a second plate is discovered above the 

 other, and almost hidden by it. The upper plate is of 

 softer texture, and furnished with many spines and bulb- 

 like projections, some of which may be connected with 

 the sense of taste (fig. 15, C). The fore-edges of these two 

 plates form the hinder border of the mouth-opening. 

 In Orthopterous insects, which with respect to the mouth- 

 parts are less specialized than most others, there are two 

 successive plates at the base of the labium, a basal and 

 larger piece, called the suhmenturiu and a distal piece, the 

 mentum, to which the terminal parts are attached. It 

 seems to us probable that the mentum of the Cliironomus- 

 larva has gradually slipped behind the submentum. 

 which now almost completely conceals it. On each side 

 of the labium is a striated and rather flexible flap (fig. 17, ?/), 

 which helps to close-in the mouth. 



The interior of the larval head is largely occupied by Orgrans en- 



. 11 closed 



the muscles of the jaws. The slender gullet passes back- within the 

 wards from the mouth into the body. The salivary ducts 

 pass forwards to open above the mentum, and behind 



