370 THE ANATOMY OF INVERTEBKATED ANIMALS. 



dinal grooved anterior face is overhung by the elongated sty- 

 liform labrum. The gnathites here exhibit almost the extreme 

 modification of the piercing and sucking type of mouth. 



Finally, the metabolous Hymenoptera, with, usually, two 

 pairs of reticulated scaleless wings, present a series of modifi- 

 cations from the essentially masticatory mouth of the Ants to 

 the partly masticatory and partly suctorial, or rather lapping, 

 mouth, such as is met with in the Bees. In the latter (Fig. 

 110) the labrum is small ; beneath it, a median fleshy lobe — 

 the epipharynx — overhangs the minute aperture of the mouth. 

 The mandibles are strong, with w T ide, almost spoon-shaped, 

 extremities. The part of the maxilla which appears to an- 

 swer to the lacinia in JBlatta is shaped like a knife-blade, 

 and folds upon the stout stip>es like a clasp-knife in its 

 handle. The short and almost rudimentary palp is attached 

 to the extremity of the stipes. The cardines are long and 

 slender, and give rise to a hinge-joint, whereby the maxillae 

 and labium can be folded back, like a carriage-step, under the 

 head. The mentum is large, the labial palps long and slen- 

 der ; there are two large paraglossse, and, between them, a 

 median, annulated, setose, cylindrical organ proceeds, which 

 either represents the lingua, or is an independent prolonga- 

 tion of the ligula. Functionally, this organ is a tongue, and 

 enables the bee to lap up the honey on which it feeds. The 

 mandibles and maxilla? are employed as cutting and model- 

 ing implements, but appear to have little or nothing to do 

 with mastication, properly so called. 



The gnathites and the mouth are abortive in some insects, 

 as the Day-flies, which take no food in the adult condition. 

 The development of the different divisions of the alimentary 

 canal varies greatly. Salivary glands are very generally 

 present. In many suctorial insects, the ingluvies is a sac 

 opening by a long duct into the gullet ; a distinct proven- 

 triculus, provided with chitinous ridges, may be present or 

 absent. The ventriculus appears to be always devoid of an 

 inner cuticula. It may be devoid of caeca or beset with short 

 cseca throughout its whole extent. The number of the Mal- 

 pighian tubes, w 7 hich are sometimes branched, varies from two 

 to a multitude. In many cases they have been found to con- 

 tain uric acid; but no biliary matter has yet been proved to 

 exist in them. Anal glands are frequently appended to the 

 termination of the rectum, and may secrete an acrid or stink- 

 ing fluid. 



