AN INSECT. 1 



body cavity so that the blood is free and "bathes" 

 the organs of the body. 



Digestion. — The digestive system includes mouth 

 cavity, salivary glands, and a crop for storage of 

 food. (This in insects with a sucking- mouth is term- 

 ed a sucking stomach, and is modified to store li- 

 quids.) Then there is a digestive stomach with or- 

 gans secreting digestive fluids, and also a large and 

 small intestine. Between the crop and the stom- 

 ach is sometimes a gizzard or small chamber armed 

 with chitinous teeth which break up the food. 



The Senses of Insects. 



Feeling. — Insects have a nervous system and a 

 rudimentary brain, hence can feel, but not to the 

 same degree as higher animals. Hearing. — Al- 

 though a knowledge of the sense is very limited, still 

 it is known that certain insects have a definite 

 hearing organ. The short horned grasshoppers 

 have an auditory organ on the ist segment of the 

 abdomen. (Plate 3, Fig. 7a.): long-horned grass- 

 hoppers have one on the tibia of each front leg. 

 (Plate 3, Fig. 6a.). Some writers think that 

 sound can be detected through the medium of the 

 antennae. Some hairs on the antennae of the mos- 

 quito have responded to vibrations of a tuning fork ; 

 the hum of the female is pitched so as to set these 

 hairs in motion. Ants and bees are said to have 

 small depressions on the antennae which seem sen- 

 sitive to sounds. Insects which have the power 

 of making the most noise have the best developed 

 organs of hearing; for example, grasshoppers, 



