NO. 



MORPHOLOGY OF INSECT SENSE ORGANS SNODGRASS 



67 



the outer edge of which 70 to 90 slender chitinous prongs (6) radi- 

 ate into the lumen of the pedicel and carry the distal attachments of 

 the sensilla. The sense cells form a thick peripheral layer in the 

 pedicel {2Seg), the distal parts of the sensilla converging toward the 

 supporting arms, while the nerves of the organ diverge from the 

 main antennal trunks {Nv) in the first segment (iScg). 



The development of the organ of Johnston in CoretJira is de- 

 scribed by Child as follows : Immediately after the last molt of the 



Fig. 31. — The organ of Johnston in simple and complex form (Child, 

 1894). 



A, longitudinal section through base of antenna of Melolontha vul- 

 garis, showing two bundles of sense cells {SCls) with terminal pro- 

 cesses attached to pits {Pi) in articular membrane between pedicel 

 {2Seg) and third antennal segment. 



B, highly developed organ of Johnston in pedicel (:?Scg) of antenna 

 of Corethra culicifonnis, longitudinal section. The terminal processes of 

 the sense cells (SCls) here attached to prongs {b) from circular chiti- 

 nous plate (a) on base of third segment (sSeg). 



larva the hypodermis of the second antennal segment forms a fold, 

 growing from before backward, that surrounds the antennal nerve. 

 The outer layer of the fold remains thin, but the inner layer thick- 

 ens by a multiplication of its cells. The cells of the inner layer then 

 become elongate, but at first are all alike ; later they differentiate 

 irito sense cells and rod-bearing cells. Nerve fibers from the central 

 nerve axis finally become attached to the bases of the sense cells. 

 This account is probably somewhat crude, but it shows at least that 

 the organ of Johnston is differentiated from the hypodermis as are 

 all other insect sense organs. 



