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N. E. McINDOO 



from the outer surface of the chitin (Ch). Each of the three 

 types of organs is supplied with a sense-cell group (SCG). 



Rohler performed no experiments, but judging merely from 

 the anatomy of these structures, he regards the bristles as tactile 

 organs which probably regulate the movements of the antenna. 

 He considers the larger or stronger pegs as tactile organs which 

 protect the body from solid objects, and the smaller or weaker 

 pegs are tactile organs which serve for the perception of wind 

 drafts. After a long discussion, he concludes that the pit pegs 

 are the olfactory receptors, and since the males have more pegs 



Figs. 90 to 92 Structure of other antennal organs of a grasshopper (Tryxalis 

 nasuta), copies from Rohler ('05); magnification not given. Fig. 90, one side of 

 next to last antennal segment (16th), showing pegs (Pg) and pit pegs (PPg), the 

 so-called olfactory organs; fig. 91, internal anatomy of pit peg, and fig. 92, same 

 of peg. Ch, chitin, and SCG, sense cell group. 



and pit pegs than have the females, he thinks that the former 

 are better equipped for finding the latter than vice versa. 



Rohler also found the sense bristles and pegs on the mouth- 

 parts, but entirely overlooked the olfactory pores on the second 

 antennal segments and on the mouth-parts. 



According to Rohler (pp. 248 and 249), the following men stud- 

 ied the antennae of Orthoptera and report the following: In 

 Stenebothrus, Kraepelin found pegs and pit pegs and in Blatta 

 only olfactory hairs (probably pegs). In Gryllidae, Locustidae, 

 and Acrididae vom Rath found both pegs and pit pegs, but in 

 Blatta and Periplaneta americana only pegs. Graber concluded 

 from his experiments that the antennae of Blatta function as 

 olfactory organs. While searching for the Johnston's organ on 

 the second antennal segments of Locusta and Stenebothrus, 



