98 INTRODUCTION TO ZOOLOGT. 



On this point the observations of Brunelli, an Italian natura- 

 list, are quite conclusive. Several of the field Crickets which 

 he kept in a chamber, "continued their crinking song through 

 the whole day; but the moment they heard a knock at the 

 door they were silent. He subsequently invented a method 

 of imitating their sounds, and when he did so outside the 

 door, at first a few would venture on a soft whisper, and by- 

 and-by the whole party burst out in a chorus to answer him; 

 but upon repeating the rap at the door, they instantly stopped 

 again, as if alarmed. He likewise confined a male in one side 

 of his garden, while he put a female in the other at liberty, 

 which began to leap so soon as she heard the crink of the 

 male, and immediately came to him — an experiment which 

 he frequently repeated with the same result." * 



There are some insects in which no organs of vision have 

 been discovered; but in general they are not only very obvious, 

 but present considerable variety in colom-, form, position, and 

 structure.! They are generally sessile; and when, to give 

 them a wider range, they are fixed, like those of many Crus- 

 tacea, on peduncles, those stalks are not moveable. The most 

 usual number of eyes is two ; but when it is needful that the 

 insect should, at the same time, have the power of 

 observing objects in the air and in the water, it is 

 gifted with four eyes, as in the common Whirl-gig 

 {Gyrinus natator. Fig. 71), which may be seen per- 

 forming its rapid evolutions on our ponds and stream- 

 lets. The eyes are sometimes simple, sometimes a 

 Fig. 71.— number of simple eyes are collected together, and are 

 Gyrinus. ^^^^ called conglomerate ; but the most common kind 

 is that which is termed compound. Such eyes, when seen 

 under the microscope, appear to consist of an infinite number 

 of convex hexagonal pieces. When separated and made 

 clean, they are as transparent as crystal. Then- number is 

 extremely variable, and cannot but strike the most iudiflfereut 

 with astonishment. " What would be thought of a quadruped 

 whose head, with the exception of the mouth and place of 

 juncture with the neck, was covered by two enomious masses 

 of eyes, numbering upwards of 12,000 in each mass? Yet 

 each is the condition of the organs of vision in the Dragon-fly." 



" Insect Miscellanies, page 77. 



t Kirby and Spence's lutroduction to Entomology, voL iiL 



