SYNOPSIS. vii 



53; specialized orders or second series from X.-XVI., 54; terms 

 *' generalized " and " specialized " substituted for " lower " and 

 " higher," 54. Hypothetical ancestor of the Thysanura described, 

 54; characteristics of this ancestor as inherited by the Thysanura 

 and the larvae of the generalized orders of insects, 54; the term 

 "Thysanuriform" preferred to " Campodeaform " or " Lepisma- 

 form," 54. Characters of Thysanura the key of modern classifica- 

 tion, 55. Representative or parallel characters of adult insects 

 the cause of mis-association of forms in older classifications, 55; 

 bearing of the hypothesis of evolution on the subject, 55. Law 

 of the correlation of the transient stages of the young with the 

 permanent adult stages of ancestral generations, 55 ; cautious use 

 of evidence necessary, 55. Theories in regard to the origin and 

 development of wings, 56; Hagen's view, 56; Fritz MUUer's . 

 and Packard's views, 56; arguments in favor of the latter, 57, 58. 

 Aquatic larvae not necessarily primitive, 58; adaptive characters 

 are secondary specializations, 58; evolution of aquatic forms of 

 insects from terrestrial forms, 58. Tracheal system of insects 

 compared with respiratory system of other animals, 59. Diffi- 

 culties attending a linear arrangement of insect groups, 60. 

 Diagrams illustrating the evolution of the orders, 60; explana- 

 tion of diagrams, 60-63; imperfections of all graphic repre- 

 sentations, 63. 



ORDER I, — THYSANURA. 



Campodecr, 64. Slight concentration of body of Campodea, 

 64. Possible sense organ in antennte, Kingsley's view, 64; long 

 antennae of cave-inhabiting species, 65. Mouth parts of gen- 

 eralized structure, 65; mandibulate and suctorial mouth parts 

 modifications of these, 65. Similarity in structure of thoracic 

 legs, 65. Absence of wings, 65. Appendages of abdomen, 

 significance of term " Thysanura," 66. Bristle-tails and Spring- 

 tails, 66. Meinert on spiracles of Campodea, 66. Lepisma 

 preferable to Campodea for class instruction, 66. Structure of 

 body of Lepisma, of appendages, 67. Respiratory system, 67; 

 presence of tracheae, absence of air-sacs in Lepisma and larvi^ 

 of insects, 67, Adult stages of Lepisma compared with tran- 

 sient larval stages of locust, etc., 67, 68. 



