INSECT MUSICIANS— SNODGRASS 451 



Schwabe, contains a transparent liquid, and both vacuole and sco- 

 lopala are traversed by a fine fiber (F) from the sense cell, which 

 ends in a dark body occupying the tip of the scolopala (G-). 



Since no two investigators have described the scolopala? or their 

 enveloping cells exactly alike, too much reliance should not be placed 

 on the details as given by any particular writer; but scolopala? in 

 similar combinations of cells are found widely distributed in special 

 organs of many insects. The so-called " ear " in the front leg of a 

 cricket or katydid has a structure essentially the same as that of the 

 abdominal organ of the grasshopper. There is an oval tympanum 

 on each side of the tibia near its upper end, and between the two 

 there are tracheal air tubes apparently giving a balanced air pres- 

 sure on both surfaces. In the crickets the tympana are exposed on 

 the surface of the leg ; in the katydids they are concealed in pockets 

 (fig. 35, E, E) opening by narrow slits on the surface (figs. 6, D, and 

 35, A, e). On the outer face of the inner trachea of the two between 

 the tympana there is a long crest, a cellular mass consisting of ex- 

 ternal cap cells (fig. 35, A, CGI), and of internal enveloping cells 

 (ECl) containing short scolopalse (Sco) and connected with a series 

 of sense cells (SOI) that receive branches from a nerve (B, Nv) 

 lying along the inner edge of the trachea. The scolopalse and their 

 containing cells in this organ decrease in size from above downward, 

 as shown at B of Figure 35, and this has suggested that they are 

 sound-receiving organs graded to respond to different notes. There 

 are other sensory cell groups associated with this structure in the 

 crickets and katydids which make the tibial organs of these insects 

 somewhat more complicated than shown in the figure. 



The connection of the scolopala-containing cells with eardrumlike 

 membranes in the Orthoptera is the principal evidence in favor of the 

 idea that they are auditory organs. But similar structures occur in 

 other insects that have no vibratory surfaces. In the legs of the 

 honeybee, as described by Mclndoo, and in other Hymenoptera there 

 are groups of cells containing scolopala?. These are connected at one 

 end with the hypodermis and at the other with a nerve and have the 

 same essential structure as the tympanal sense body of the grass- 

 hopper, except for the lack of the tympanum. Likewise some insect 

 larva? have similar cell structures in the sides of the body segments, 

 but these are suspended by cords and have received the name of 

 chordotonal organs. 



Experimental evidence of the hearing powers of insects is at pres- 

 ent very meager, but it would be surprising if insects do not hear the 

 sounds they themselves produce. Many insects have sense organs in 

 the second joint of the antenna, which are most highly developed in 



