364 THE LOCUST 



tion must be at a certain rate to cause a response. A flying insect 

 moving rapidly at some distance from the ground, as does the 

 honey-bee in its homeward journey, would find such a form of 

 vision well adapted to the recognition of the landmarks by which 

 it is assumed the animal directs its course. In view of their 

 structural relationships, it has sometimes been maintained that the 

 compound eyes of arthropods have arisen as collections of spe- 

 cialized ocelli. This theory is now regarded as untenable by most 

 students of the Arthropoda. It seems more probable that ocelli 

 and compound eyes are both derivatives of primitive visual organs 

 that existed in the common ancestors of insects and crustaceans. 



That insects have a color sense in some instances can be shown 

 by simple observations and experiments, but the range may differ 

 from our own. Ants, for example, will avoid violet light as they 

 will sunlight, and they seem not to distinguish red or orange light 

 from darkness. Again, they are very sensitive to ultra-violet 

 light, to which man gives no conscious responses. It also appears, 

 although the odor may be presumed to be an additional factor, 

 that bees and moths may be somewhat influenced by color in their 

 choice of flowers. 



Before considering the sense of hearing in the grasshopper and 

 ether insects, something may be said regarding the power of sound 

 ^production which exists in almost every insect possessing struc- 

 tures that can be anatomically regarded as auditory organs. The 

 sounds produced by the rapid vibrations of the wings, as in a mos- 

 quito, need not be considered, since they are incidental to other 

 activities and are not caused by special sound-producing organs. 

 An example of the latter, in an insect closely related to the grass- 

 hopper, is the siridulating organ of the katydid, Microcentrum 

 laurifolium (Fig. 184). In the male, the left mesothoracic wing, 

 which is developed as a wing-cover, bears an elongated ridge with 

 many transverse elevations, the "file," and the right wing, 

 a ridge-like " scraper." In sound production the wings are 

 sHghtly separated, and as they are drawn lightly together the 

 scraper is rubbed across the file, giving a series of sharp " tics " 

 in rapid succession. The sound thus produced is a sex call by 

 which the female is guided to the male. There is also a short 

 " chirp " which may be made by opening the wing-covers. The 

 chirp of a cricket is produced in a similar manner. There are 

 many forms of stridulating organs in insects. In the common 



