INSECTS. 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 cirii. 
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 Astacide” (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. gor; “‘ Barnacles,” J. S. Kingsley, “ Ameri- 
can Naturalist,” vol. xi, p. 102; “The Cray-fish,” Huxley. 
Class II.—INsSEcTS (Jusecta). 
General Characteristics—Arthropoda, with the head, 
thorax, and abdomen distinct ; breathing by air-tubes or 
trachee ; the young passing through changes called a met- 
amorphosts. 
Skeleton.—The skeleton (Fig. 110) 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 /edrum ; 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 /adiuvm, is in reality a pair of 
jaws, and to it are attached another pair of jointed feelers 
