230 PRINCIPLES AND CONCLUSIONS. 



antennae, or these entire appendages, or varnished them with paraffin, rubber, and 

 so forth. When a few joints are severed, the sense of smell is apparently weakened. 

 This is true for bees also. When both antennae are amputated or varnished, the in- 

 sects as a rule fail to respond to substances which normally affect the olfactory sense. 

 They generally fail to respond to odors held near them and fail to find food in cap- 

 tivity, and do not return to putrid meat and dead bodies when removed from such 

 food. Males so mutilated as a rule do not seek females and show no responses when 

 females are placed near them. Such experiments were seriously criticised until Hauser 

 in 1880 presented his apparently conclusive results. Many of the insects on which he 

 experimented with the antennae amputated became sick and soon died. Most of 

 them failed to respond when the antennae were mutilated, although Carabus, Melo- 

 lontha, and Silpha responded slightly, while all the Hemiptera that he used responded 

 almost as well with their antennae off as they did with them intact. Only 40 per 

 cent of the ants from which Miss Fielde cut the antennae recovered from the effect 

 of the shock. Not one of these observers has studied the behavior of the species 

 under observation sufficiently to know exactly how long they live in captivity with 

 their antennae either intact or mutilated. No one, except Miss Fielde, has kept a 

 record of the death of the mutilated and normal insects so accurate that one might 

 know what percentage died from the operation. To cut off some other appendage 

 or even the lower part of the head, as Forel did, is not a fair test, because such oper- 

 ations seldom expose sense-cells and never any nerve equal in size to that of the an- 

 tennae, unless one pulls off the wings. When the wings are pulled off, the large nerve 

 is severed between the masses of sense-cells and the thorax, and the sense-cells are 

 not exposed to the air, as they are when antennae are removed. Even if the an- 

 tennae are cut through the scape, the large masses of sense cells belonging to John- 

 ston's organs are severed. When the lower part of the head or the tarsi are cut off, 

 as Forel did, no nerves are exposed to the air except ends of small nerves. From the 

 foregoing it is only reasonable to assume that when the antennae of any insect are 

 injured in the least degree, the insect is no longer normal and if it fails to respond 

 to odors placed near it, this negative response may be due to the shock of the injury." 



Present status as to the seat of the olfactory sense. — In spite of 

 the obvious merits of Mclndoo's studies, it is evident that further in- 

 vestigations will be necessary to decide the respective claims of the an- 

 tennae and the olfactory pores as the organs of smell. The results of more 

 than a score of investigators, some of them, such as Forel, Graber, Hauser, 

 and Plateau, of the first rank, are in accord as to the olfactory function 

 of the antennae, and it is certain that their conclusions can not be rejected 

 without a repetition of their most decisive experiments. On the other hand, 

 many of Mclndoo's are similarly decisive, and at present it seems quite 

 possible that both antennae and pores have to do with smell. The burden 

 of proof rests upon the latter, however, since they lack the confirmation 

 given by successive investigators to the function of the antennae. Mcln- 

 doo has given a practically complete list of those who have based their 

 conclusion as to the olfactory function of the antennae upon experi- 

 mental evidence (1914 3 :14). They are Dug6s (1838), Lefebvre (1838), 

 Ktister (1844), Perris (1850), Cornalia (1856), Donhoff (1861), Balbiani 

 (1866), Forel (1874, 1878, 1886, 1901), Trouvelot (1877), Layard (1878), 

 Slater (1878), Chatin (1880), Hauser (1880), Porter (1883), Graber (1885, 

 1887), Plateau (1886, 1902), Dubois (1895), Mayor (1900), Gorka (1900), 

 Fielde (1901, 1903), Barrows (1907), and Kellogg (1907). The most ex- 

 tensive and significant studies have been those of Forel, Hauser, Graber, 



