AN INTRODUCTION TO ENTOMOLOGY. 



greatly in different insects, as is shown by the accompanying 

 figures.* 



What are supposed to be organs of taste in Hymenoptera and 

 Diptera have been carefully described by Will.$ These consist of 

 pits on the labium and on the lower side of the maxillae through 



FIG. 



49. Organ of taste in the labium 

 of Vespa vulgaris. (After Will.) 



FIG. 50. Similar organ in maxilla of the 

 same insect. (After Will.) 



Lettering of Figs. 49 and 50. C, cuticle; P, pit in the same; Sc, sense-cell; Ne, neurilemma of sense- 

 cell; Ac, axis cylinder of sense-cell; E, end of the same; N, nerve connected with sense-cell; M, 

 matrix-cells; Gc, gland-cells. 



which ends of nerves come to the surface. The structure of these 

 organs in Vespa vulgaris is shown in Figs. 49 and 50. 



It is probable \hz\.' organs of 

 touch are well developed in many 

 insects. Leydig, Hicks, and Vial- 

 lanes have described tactile hairs, 

 which are situated upon pores in 

 the cuticle, in which nerves end. 

 Figure 51 is a diagram of one of 

 these hairs. 



The Respiratory System. If an 

 insect be carefully examined there 

 can be found along the sides of the 

 body a series of openings. These can be easily seen in many cater- 

 pillars and other larvae; they are the openings of the respiratory sys- 

 tem, and are termed the spiracles. 



The number of spiracles varies greatly in different insects. 

 There is, however, never more than one pair on a single segment of 

 the body. They do not occur on the head, but are borne by each 

 of the thoracic segments, and by the first eight abdominal segments. 

 Thus there are eleven segments that may bear spiracles ; but they 

 are always lacking on some one or more of these. 



* For generalizations regarding these organs see Kraepelin, translated by Packard, 

 American Naturalist, 1887, p. 182. 



\ Will, F. Das Geschmacksorgan der Insekten. Zeitschrift fiir Wissen. Zool. 

 1885, p. 674. 



FIG. 51. Diagram of tactile hair, c, cuticle 

 hy, hypodermis; bm, basal membrane; h 

 hair; he, hair-cell; , nerve; nc, nerve-cell. 



