ARTHKOPODA. 105 



some of the lowest forms of insect-life, and Hymenoptera pro- 

 bably the highest ; between these it is scarcely possible to arrange 

 the remaining orders in any thing like a satisfactory manner. 

 There cannot be said to be any connecting links between them, 

 although superficial resemblances may in a few instances be ob- 

 served. 



Hackel, according to his views of the succession of insect-life 

 on the earth, places the orders in this sequence: Archiptera, 

 Neuroptera, Orthoptera, Coleoptera (these orders hare mandi- 

 bulate mouths, and were the only insects existing for a long 

 period ; the last three, he continues, were probably derived from 

 the Archiptera, i. e. Ephemera, Libellula, Lepisma, Termes, &c.), 

 Hymenoptera, Hemiptera, Diptera, and Lepidoptera. An ancient 

 fly (Eugercon) in the Permian system seems to indicate, he 

 thinks, the derivation of the Hemiptera from the Neuroptera. 

 Gerstaecker (1873) begins with the Orthoptera aud ends with 

 the Hemiptera, placing Hymenoptera in the middle as the highest 

 type of the insect-forms. 



Fritz Miiller thinks " that the most ancient insects " approached 

 most nearly to the wingless Blattidae, and that the complete 

 metamorphoses of Diptera, Lepidcptera, Coleoptera, &c. were 

 of lat'er origin, and that there were perfect insects before larvie 

 and pupas. 



A sequence based on fossil remains would, at present, be un- 

 satisfactory, seeing that at least one Coleopteron (allied to the 

 Curc-ulionidse) has been found in the Coal-measures, and so far is 

 among the oldest known insects. 



Order I. COLLEMBOLA. 



Thorax of three, abdomen of six segments ; the anterior abdo- 

 minal segment with a ventral tube or sucker beneath, the penul- 

 timate segment with saltatory appendages. Antennae few-jointed. 

 Wingless. No metamorphosis. 



The eyes consist of ' ' distinct ocelli." Templetonia has one ocellus 

 on each side, and Smynthurus and some others eight. The mouth 

 is not very distinctly mandibulate, and in Anurida it is suctorial. 

 The trachea; are in general well developed. The saltatory appen- 

 dages consist of two long processes bent under the body and held 

 by a small catch ; directly this releases its hold, the spring jerks 

 back, and the creature is thrown upwards and forwards. The 

 tube or sucker contains a viscous fluid. The body is clothed either 

 with hairs or with scales. 



