588 THE SENSES AND SENSORY ORGANS 



between them --the so-called pore plates of which each 

 antenna has from 17,000 to 18,000. These are about 5 /j. in 

 diameter (Fig. 72, E). 



Sections show that the pore-plates are the orifices of flask- 

 shaped canals (PI. XLI., Fig. 2, A). The canals are sur- 

 mounted by transparent sensor)- setae, 50 ^ in length. These 

 sensory setae are nearly straight ; they are conical, and in 

 many preparations exhibit the appearance of having a slit 

 running down one side and ending toward the apex of the seta 

 in an oblique opening. Each contains a process from a 

 ganglion cell, which is partially embedded in the pore canal. 

 These setae are very easily detached, and leave their contents 

 projecting from the pore canal as a flame-shaped process the 

 olfactory cone of authors. Sometimes the term ' olfactory 

 cone ' has been applied, however, to the seta. In a few pre- 

 parations I have observed a fine axis cylinder only projecting 

 from the pore canal ; but I believe, like the flame-shaped 

 cones, this is only the result of the detachment of the seta 

 from its base, the greater part of its contents having been torn 

 away with the seta itself. All these conditions have been 

 figured by Krapelin, who took them for modifications of a 

 typical seta. 



The short, thick, opaque setae which spring directly from 

 the epidermal cuticle are only about half as long as the sensory 

 setae. Their function is probably to protect the bases of the 

 sensory setae. 



The arrangement of the hypodermal and ganglionic cells 

 beneath the cuticle will be readily understood by a reference 

 to the figures (PI. XLI., Figs, i and 2). 



The subcutaneous ganglion cells are the superficial layer 

 of the terminal ganglion of the antennal nerve ; beneath these 

 there are numerous layers of far smaller round cells, which 

 form its deep layer. This ganglion consists of a continuous 

 layer, 50 jj, or 60 p, thick, over the whole inner surface of the 

 integument of the third joint of the antenna. Its cells are sup- 

 ported and bound together by a fine reticular stroma. Some of 

 the terminal branches of the nerve can be traced directly to 



