64 . ixrs. 



Janet ( 1904) has recently studied their structure with great care, 

 and has not only added many details to those seen bv his pre- 

 dece>rs, but has al><.> discovered a number of less conspicuous 

 chordotonal organs in other parts of the ant's body. He finds a 

 pair in the head at the base of the antennae (Fig. 27, achot, one 

 in the prosternum. just under the prothoracic ganglion (clw). with 

 which it is connected by short nerves, a similar pair in the metasternnm 

 and two pairs, one in the petiole and another in the postpetiole, which 

 lie near the tracheal stigmata and are innervated by the ganglia of 

 their respective segments. Eight pairs of chordotonal organs have, 

 therefore, been seen in the ant's body, but it is not improbable, as Tanet 

 suggests, that others exist, for such minute and recondite objects are 

 very easily overlooked even in well-prepared sections. I find that the 

 tibial organs (Fig. 33) are very easily seen in light-colored ants that 

 have been simply mounted in alcohol, and that they are clearer in males 

 than in workers or females. In clove oil, or Canada balsam, however, 

 the structures are seen only with difficulty and after they have been 

 located in alcoholic specimens. 



The Johnstonian Organ. This peculiar structure, first described by 

 Johnston in 1855. an d since carefully investigated by Child (1894). is 

 very similar to the chordotonal organs. It is found only in the second 

 antennal joint of insects and seems to reach its highest development in 

 certain Orthorrhaphons Diptera (gnats). Child found it also in the 

 ETymenoptera (Formica, J^cspa. Boinbits) and Berlese has published 

 some good figures of it in the hornet. I find that it is decidedly larger 

 in male than in worker and female ants, especially in those genera like 

 Phcidolc and Solenopsis, in which the males have an unusually swollen 

 or globular second antennal (first funicular) joint. Janet seems to 

 have overlooked the Johnstonian organs in the Mynnica. which he has 

 studied so exhaustively. In section the organ is seen to consist of a 

 variable but considerable number of sensilke differing but slightly from 

 those of the chordotonal organs, and also containing scolopal bodies. 

 These sensillae are stretched more or less parallel with the long axis of 

 the funiculus. through the cavity of the second joint. Their distal or 

 hypodermal ends are attached to the articular membrane between the 

 second and third joints, while their proximal ends are innervated by a 

 portion of the antennal nerve. They form a compact cylinder enclos- 

 ing the remainder of the nerve which passes on into the more distal 

 antennal joints. Both Johnston and Child are inclined to regard the 

 sense-organs under discussion as auditory, although the latter believes 

 that their more primitive function is tactile. As will be shown in 



