1919] 



Mclndoo: Olfactory Sense 



81 



Nagel (1894) called the small hairs at the tip of the antennae 

 (Fig. 1, THr) of a lepidopterous larva olfactory pegs, but in 

 the opinion of the present writer they are nothing more than 

 tactile hairs. Sections through them show that they are not 

 true hairs, because they do not arise from sockets, but each one 

 is nevertheless innervated ; the larger ones seem to be provided 

 with sense cell groups (Fig. 49, SCG), while the smaller ones 

 (Fig. 50, THr) arising from the dome seem to be provided with 



Figs. 49 and 50. — Longitudinal sections, showing internal anatomy of antenna 

 of tomato worm. Fig. 49, the larger type of one of Nagel's so-called olfactory 

 pegs at tip of antenna, X 500; sense-cell group (SCG). Fig. 50 shows how well 

 antenna is innervated; semidiagrammatic, X 100. Hypodermis (Hyp); nerve 

 (N); antennal pore (Anta); probably hair-mother cell (HrMC); sense cell 

 {SC), connected with pore; sense cell (5Ci), connected with peg; smaller 

 type of one of Nagel's so-called olfactory pegs {THr) arising from dome; 

 and base of large true hair {Hr). 



single sense cells {SC\). The large hair {Hr) at the tip of the 

 antenna is a true hair, but it does not appear to be sensory, 

 although lying at its base there are one or two large cells {HrMC) 

 which resemble hair-mother cells more than sense cells. 



One author draws the antennae of lepidopterous larvae as if 

 they were composed of 3 or 4 segments, but sections show 

 only two distinct segments in each, although sometimes the 

 basal one is so folded that indications of two more segments 

 are visible, as shown in Figure 50, which also gives a good idea 

 of how well the antenna is innervated. 



