NO. 8 MORPHOLOGY OF INSECT SENSE ORGANS SNODGRASS 63 



In the wing bases, including the halteres of Diptera, it is now 

 known that chordotonal organs are of frequent occurrence. The 

 studies of Pflugstaedt (1912), Vogel (1912), Lehr (1914) and 

 Erhardt (1916), show that they are present in this location in Odo- 

 nata, Neuroptera. Coleoptera, Lepidoptera, Diptera, and Hymenoptera, 

 but absent in Orthoptera and Hemiptera. Usually, each wing base con- 

 tains only one or two organs, though Erhardt reports the presence 

 of seven in the base of each front wing of Chrysopa, and six in 

 each hind wing. The distal ends of the wing organs are in all cases 

 attached to the ventral surfaces of the wing bases. 



In other parts of the body, chordotonal organs have been de- 

 scribed in various situations in different insects : in the head of ants 

 and bees (Janet, 1894, 191 1), in the antennae of Dytiscus (Lehr, 

 1914), in the ventral part of the prothorax of ants (Janet, 1894), 

 in the posterior part of the thorax of many Lepidoptera (Eggers, 

 1920), and in the first abdominal segment of the cicada (Vogel, 

 1923 a). Judging from the number of chordotonal organs already 

 known in insects, and from the diversity of their positions, it is 

 likely that further studies will show a still wider distribution of 

 them in a greater number of species. It would be surprising, 

 in fact, if they should not be found eventually in most of the species 

 in all orders. 



The development of the chordotonal organs in the legs of the 

 honeybee has been studied by Schon (1911). In the worker bee, 

 according to Schon's account, on the eighth day after the laying of the 

 egg, which is the fifth day of the larval stage, there appears in the 

 tibia of the inverted imaginal leg, just below the femero-tibial joint, 

 a small ingrowth of the hypodermis over an invagination of the cuti- 

 cular wall of the leg. This ingrowth becomes the chordotonal organ. 

 On the ninth and tenth days its cells begin to differentiate, the sense 

 cells being first distinguishable, segregated at the inner end of the 

 mass. From them a short process extends inward which will later 

 unite with the chordotonal branch of the leg nerve. The imaginal 

 bud of the leg is everted on the eleventh day. On the thirteenth day 

 there still remains a remnant of the cuticular invagination ; the ex- 

 ternal opening is finally closed, but the internal part remains as a 

 hollow within the mature organ. On the seventeenth day the organ 

 is completed ; on the twenty-first day the young worker emerges 

 from its cell. From this account it is clear that the chordotonal organ 

 is a modification of the body wall, as are all the other sense organs, 

 and that its cells, including the sense cells, are dift'erentiations of 

 the hypodermis. 



