32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 63 



perception. Formica (an ant) has far more pegs than pore plates, 

 contrary to the rule in hymenopterous insects. In conclusion Hauser 

 asserts that in almost all insects the olfactory organ consists of (i) 

 a large nerve arising" from the cephalic ganglion which runs out 

 into the antenna, (2) a recipient end apparatus which represents 

 rod cells modified from hypodermal cells with which the fibers of 

 those nerves are connected, (3) a supporting and accessory appara- 

 tus which is formed by the pore plates and pegs filled with a serous 

 fluid. When both pore plates and pegs are present they both function 

 in smelling according to their number ; when one of these organs is 

 absent then the other one functions entirely as an olfactory receptor. 



Krapelin (1883), according to Schenk (1903), considers the pore 

 plates and pegs as smelling organs and translating from Vom Rath 

 (1888) Krapelin thinks that the olfactory organ is also located in the 

 palpi. 



Schiemenz ( 1883) regards the pegs as touch organs, while the pore 

 plates and Forel's flasks probably serve as olfactory organs. 



Sazepin (1884) worked chiefly on the antenna? of myriapods, but 

 he also spent some time in working out the anatomy of the antennae 

 of Vespa. By comparing the anatomy of the myriapods' antennae 

 and with that of Vespa he found that as a whole there is a great sim- 

 ilarity, but while the olfactory pegs in Vespa are closed at their tip, 

 they are open in what he calls the olfactory pegs in myriapods. 



Witlaczil (1885) worked on the antennae of certain bugs. Since 

 their antennal^ pits, called olfactory pits by Hauser, are covered by 

 a membrane he thinks that they can scarcely be called olfactory 

 organs. 



Vom Rath (1887, 1888), like most authors on this subject, regards 

 the olfactory sense as located in the sense pegs of the antennae and 

 probably also in the pore plates. By making a comparative study of 

 all the antennal organs in arthropods, Vom Rath (1895) found a 

 great similarity in the structure of each set of organs. The sense 

 pegs are not by any means confined solely to the antennae but are 

 found on all the mouth parts, in the mouth cavity, and even over the 

 entire body. It is possible that many pegs serve for the reception of 

 the stimuli of weak odors from a distant object and others for the 

 olfactory perception of those nearer. It may be that the pegs of 

 each kind, and also the pore plates, are especially responsive to 

 certain kinds of odors. He believes that the pegs on the palpi possess 

 an olfactory function and possibly for odors close at hand. More- 

 over, these pegs elsewhere may have the same function. 



