IA T SECTS. 



97 



scopic examination. The ear and other organs should re- 

 ceive particular attention. The smaller crustaceans found 

 in ponds, etc., should be examined alive under the micro- 

 scope. Barnacles can be found on oyster-shells at any 

 restaurant, and when placed in water show their cirri. 



Works on Crustaceans for further reference. 



" Challenger Reports " ; "A Naturalist's Sojourn in Jamaica," 

 Gosse ; " Crustacea of the United States Exploring Expedition," J. D. 

 Dana ; " North American Astacidae " (Fresh-water lobsters), H. A. 

 Hagen, in " Memoirs of Museum of Comparative Zoology," vol. ii, 

 No. 3, 1871 ; " Habits of certain Cray-fish," C. C. Abbott, " American 

 Naturalist," vol. ix, p. 80 ; " Descriptions of the North American Phyl- 

 lopoda," A. S. Packard, Jr. ; " Report of Hayden's Survey," 1873, p. 

 613 ; " Report of Peabody Academy of Sciences," 1873 ; " Report of 

 United States Commissioner of Fisheries," 1874 ; "Crustacea," S. J. 

 Smith ; " The Lobster and Lobster-Fishing," W. W. Wheildon, " Pro- 

 ceedings of American Association for the Advancement of Science," 

 vol. xxiii, 1874 ; " Early Stages of the Lobster," " Popular Science 

 Monthly," vol. iii, 1872, p. 401 ; " Barnacles," J. S. Kingsley, " Ameri- 

 can Naturalist," vol. xi, p. 102; "The Cray-fish," Huxley. 



Class II. INSECTS (Insect a). 



General Characteristics. Arthropoda, with the head, 

 thorax, and abdomen distinct ; breathing by air-tubes or 

 tracheae ; the young passing through changes called a met- 

 amorphosis. 



Skeleton. The skeleton (Fig. no) is external, and 

 composed of a horny substance called chitine. As in the 

 crustaceans, the body is made up of segments, numbering 

 in the winged forms generally four in the head, three in the 

 thorax, and ten or eleven in the abdomen. The mouth- 

 parts of insects consist, as a rule, of four separate divi- 

 sions ; namely, the upper lip, or labrum ; a pair of crushing 

 or cutting jaws (mandibles) ; and a smaller pair (maxilla), 

 to which small jointed feelers called maxillary palpi are 

 attached. The lower lip, or labium, is in reality a pair of 

 jaws, and to it are attached another pair of jointed feelers 



