268 TEXT-BOOK OF ENTOMOLOGY 



the perception of odors. It comprises a structure composed of nervous sub- 

 stances which are enclosed in a chitinous tube, and either only stand in relation 

 to the surrounding bodies by the perforated point, or pass to the surface as free 

 nerve-fibrillpe. 



In insects there is a remarkable and fundamental difference in the structures 

 of the parts supposed to be the organs of smell. Erichson was acquainted only 

 with the " pori " covered by a thin membrane; but Burmeister, in his careful 

 work on the antennae of the lamellicorns, distinguished pits at the bottom of 

 which hairs rise from a cup-like tubercle, from those which were free from 

 hairs. Leydig afterwards was the first to regard as olfactory organs the so- 

 called pegs (kegel"), a short, thick, hair-like structure distinctly perforated at the 

 tip, which had already, by Lespes in Cercopis, etc., been described as a kind of 

 tactile papilla. Other very peculiar olfactory organs of different form, Forel 

 (Fourmis de la Suisse) discovered in the antennae of ants, which Lubbock incor- 

 rectly associated with the nerve-end apparatus found by Hicks in other insects. 



As the final result of his researches Kraepelin states that the 

 great variety of antennal structures previously described may be re- 

 ferred to a single common fundamental type of a more or less devel- 

 oped free or sunken hair-like body which stands in connection by 

 means of a wide pore-canal with a many-nucleated ganglion-cell. 

 The latter sends only a relatively slender nerve-fibre (axial cord) 

 through the pore-canal into the hair; but the same is enclosed by 

 epithelial cells which surround the pore-canal. 



Mauser's researches on the organs of smell in insects were so 

 carefully made and conclusive that our readers will, we feel sure, be 

 glad to have laid before them in detail the facts which prove so 

 satisfactorily that the antennae of most insects are olfactory rather 

 than auditory in their functions. 



Physiological experiments. --First of all one should observe as 

 exactly as possible the normal animal in its relation to certain odor- 

 ous substances, whose fumes possess no corrosive power or peculiari- 

 ties interfering with respiration ; then remove the antennae and try 

 after several days to ascertain what changes have taken place in the 

 relation of the animal to the substance. In order to come to no false 

 results it is often necessary to let the insects operated iipon rest one 

 or two days, for immediately after the operation they are generally 

 so restless that a careful experiment is impossible. 



The extirpation of the antennae is borne by different insects in 

 different ways; many bear it very easily, and can live for months 

 after the operation, while others die in the course of a few days 

 after the loss of these appendages. The animals seem to be least 

 injured if the operation is performed at a time when they are hiber- 

 nating. J't/rrliororis apterus, and many other insects, afforded a very 

 striking proof of this relation. 



