on the Mouths of Insects. 23 



other orders in which the excessive development of some organs 

 is more marked. 



A typical mouth consists of a pair of mandibles working 

 laterally, covered by a roof-piece called the labrum. Below the 

 mandibles are another pair of jaws, the maxillae, with the lower 

 lip, the labium. Both the latter have appendages called palpi. 



CoLEOPTEEA. — Beginning with the mandibles, we find three 

 forms: carnivorous (tiger beetle), vegetable (cockchafer), insecti- 

 vorous (dragonfly). In each case they are unjointed, move 

 backwards and forwards only by a ginglymus joint, and have no 

 appendages, except a small feathered cartilaginous process found 

 in the Staphylinidse, and known as the prostheca, and a yellow 

 sac, which occurs in Blaps, the use of which is not apparent. 



The maxillae are more elaborate, and are composed of a num- 

 ber of joints, and exhibit great variety in form. Attached are 

 the maxillary palpi, which in some of the carnivorous groups 

 are in duplicate, and it is here especially that many of the sense 

 organs exist. 



The labium closes the mouth below, and shows great develop- 

 ment in some of the Orthoptera. It bears the labial palpi, which 

 usually have fewer joints than the maxillary palpi. The various 

 parts of this organ may be studied better in other orders. 



Hymenoptera. — Form an intermediate step between the 

 mandibulate and haustellate, partaking of the character of both; 

 for, in addition to mandibles, we find a great development of the 

 ligula or tongue. In the bees great variation of the latter is met 

 with, forming two groups, the short and long tongued ; and in 

 the photographs now shown the details can be understood, and I 

 would refer any one desiring a full knowledge of this interesting 

 point to Cheshire's admirable book on bees. 



Hemipteka. — This order is distinctly one of the haustellate 

 group. The head is prolonged into a beak or rostrum composed 

 of an elongated labrum and labium united. The mandibles are 

 very fine and lancet-like, while the maxillae, equally fine and 

 closely united, appear as one organ. The rostrum is frequently 

 very long and folded beneath the body. 



Diptera. — Here we find the labrum and labium united to form 

 a tube, and, as very great variety exists, we will select two 

 types :— 



1. Gnat. Trophi in female adapted for piercing and con- 

 sisting of mandibles and maxillte reduced to fine bristle-like 

 organs, and which, together with the labrum, enter the wound. 

 The labium is the largest piece, and forms a trough, in which 

 the others lie, and which merely doubles up, but does not enter 

 the wound when the puncture is made. In many parts of the 



