INSECTS. 509 



most destructive in spring. The larvae are but seldom 

 seen, being careful to conceal themselves in the bodies they 

 attack, and their presence can only be guessed at by 

 finding occasionally their cast-off skins, which they change 

 several times during their larvae state. Whenever, there- 

 fore, little rolls of black skins are found near where ham 

 or bacon is kept, or in cases containing objects of natural 

 history, it is more than probable this beetle has there 

 taken up its abode. The small scales covering many species 

 of Dermestes y as well as hairs, are beautiful microscopic 

 objects, and may be mounted in the dry state. 



In the Gyrinus, Whirligig, we have a combination of 

 contrivances to facilitate the creature's movements in the 

 element it lives in. The hind legs are converted into 

 a pair of oars of remarkable efficiency, the point of their 

 connection with the body being adapted with great preci- 

 sion to ensure the most effectual application of the propel- 

 ling power; as it strikes out behind in the act of 

 swimming, a membranous expansion of a, portion of the 

 legs enables the insect to move about with great rapidity; 

 upon the legs being drawn back again towards the body, 

 the membrane closes up, and thus offers but a small 

 resistance to the water (fig. 265). If the insect wishes to 

 remain below the surface of the water, he employs the 

 small hooks placed at the extremity of the feet for the 

 purpose of holding on to the roots or stems of aquatic 

 plants. The eyes are not the least curious part of the 

 merry little creature ; the upper portions of them, being 

 fitted for seeing in the air, are fixed on the upper part 

 of the head, while the lower portion, fitted for seeing in 

 water, are placed at the lowest part, a thin division 

 separating the two. 



Hemiplera, or ffeteroptera, Bugs, form two principal 

 groups, distinguished by their structure and habits, the 

 Hydrocores, Water- bugs, and the Geocores, Land- bugs. The 

 latter never possess wings : the disagreeable Bed-bug (Cimex 

 lectularius) is the typical form of this group. The former 

 are recognisable by the small size of their antennae, which 

 are divided into three or four short joints, and are con- 

 cealed beneath the eyes. Of these, the Notonectida are 

 distinguished by their broad, rounded head, which occu- 



