OLFACTORY ORGANS OF A COLEOPTEROUS LARVA 119 



dible. The chitin around the cones and pore cavities has assumed 

 a yellowish color, causing variously shaped formations; these are 

 represented by solid black in the drawings. The simplest forma- 

 tion surrounds only the cone as shown in figures 1, 3 to 5; another 

 type surrounds all of the cone and a part of the pore cavity as 

 shown in figures 9 and 10; and the most complex type surrounds 

 all of the cone and practically all of the pore cavity as may be 

 observed in figures 2, 6, 11 to 13. 



b. Compound olfactory organs. In longitudinal sections through 

 the last segment of the antenna large groups of sense cells lie in 

 deep indentations of the chitin. At the outer ends of the sense 

 cells the plate of chitin is extremely thin, thus allowing the light 

 to pass throiigh it more readily when the integument, treated 

 with caustic potash, is examined; this explains the presence of 

 the large light spots on the distal segments of the antennae, 

 already mentioned. During a closer examination under the oil- 

 immersion lens, a few minute pore apertures (fig. 14, PorAp) 

 were seen passing through this thin chitin, and a thin cone 

 (Con) is also invariably present. The sense cells (SC) are very 

 long and slender, and are closely compact. Most of them may be 

 cut longitudinally, but several may be cut crosswise, indicating 

 that the latter may run to another plate. The outer ends of 

 them are often seen running into the pore apertures, while the 

 inner ends sometimes pass into the lumen of the antenna. The 

 entire group of sense cells is always surrounded by a neurilemma 

 (Neu). 



Cross sections through the last segment of the antenna, will 

 show one or more large g oups of sense cells. The cross section 

 represented by figure 15 is typical; attention is called to the four 

 groups of sense cells in the ventral portion (upper side of the 

 figure) of the antenna; to the five branches of the nerve, surround- 

 ed by many small bodies, presumably metamorphosing cells, in 

 the middle of the lumen ; to the small portions of three groups of 

 sense cells in the dorsal part (lower side of the figure) of the 

 antenna; and to a single olfactory pore in the chitin on the dorsal 

 side. Since thin places in the chitin are shown only at the top of 

 this drawing, the chitinous plates {PI) belonging to the sense 



