226 MANUAL OP ZOOLOGY. 



feet, but with a horny head, which it protrudes from between 

 the abdominal segments of its host. The larvae are active, and 

 possess six feet ; whilst the males are winged and fly about 

 with great activity. 



ORDER XII. COLEOPTERA. Mouth masticatory, furnished 

 with mandibles and maxillae. Wings four; anterior pair chi- 

 tinous, forming protective cases (elytra) for the large, mem- 

 branous posterior wings (jig. 70): 



Fig. 70. Coleoptera. Dytiscus marginalis, a common British water-beetle. 



The order Coleoptera includes all those Insects known com- 

 monly as ' Beetles,' comprising an enormous number of species 

 and genera. 



The larvae of the Coleoptera are vermiform grubs, with masti- 

 catory mouths, usually three pairs of thoracic legs, and often 

 anal pro-legs. 



DISTRIBUTION OF INSECTA IN TIME. The earliest known in- 

 sects have been discovered in the Devonian Rocks of America, 

 and consist of the remains of Neuroptera. Others, as might 

 have been anticipated, have been found in the Coal-measures. 

 In the Secondary Rocks remains of Insects have been found 

 abundantly in certain beds of the Oolitic and Liassic formations. 

 In some Tertiary strata Lepidoptera and other insects have 

 been found in a good state of preservation. Amber, which is 

 a fossil resin, has long been known to contain many insects in 

 its interior (in certain specimens) ; and all of these appear to 

 belong to extinct species, though amber, geologically speaking, 

 is not an ancient product. 



