Olfactory Organs of Spiders. 335 



found the plate always dry. I liave even captured some 

 when engaged in sucking a tlj, and on examining them could 

 not observe any trace of a fluid upon the plate. 



We are therefore driven to the conclusion that it is a sense- 

 organ, and in this conclusion we are strengthened by the 

 presence of a strong nerve. Let us then run over the series 

 of our senses and inquire for what sense the organ seems to 

 be best adapted. 



The sense of touch is at once excluded, because there are 

 no projecting parts, and, moreover, the extremity of the max- 

 illge is abundantly furnished with tactile hairs (fig. 4, t). The 

 position alone seems to be little in favour of its being an 

 auditory organ, as the surface is completely concealed by the 

 mandibles, whilst an auditory organ is usually placed as 

 0[)enly as possible upon the surface. Further, we have 

 already seen reason to regard the hairs above described as 

 organs of hearing. 



The notion of an organ of taste seems to be favoured by 

 the position on parts of the mouth. Nevertheless, as already 

 mentioned, the porous surface remains perfectly dry during 

 the sucking of an insect. We should therefore rather regard 

 as taste-cells a group of cells situated on the anterior surface 

 of the suctorial groove (which can be closed as a tube), and 

 therefore in the labrum. These cells also receive a nerve 

 which springs from the supra-oesophageal ganglion and runs 

 above the oesophagus. 



Thus for our organ there remains only the interpretation as 

 an olfactory organ, unless we are inclined, without any 

 foundation, to assume the existence of a sense that is defi- 

 cient in ourselves. The position would certainly be very 

 suitable for an organ of smell ; for as the plate is covered by 

 the mandibles, it is protected from complete desiccation. The 

 condition that the membrane of the olfactory cells, with which 

 the particles come into contact, must be moist, could there- 

 fore here be fulfilled. 



That the sense of smell is of importance to spiders, as to 

 all air-breathing animals, needs no proof; it is, indeed, the 

 principal purpose of this sense to test the air that is breathed. 

 This principal function furnishes us with a ready means of 

 convincing ourselves of the existence of a sense of smell. 

 The animal will instinctively avoid all strong odours. I have 

 experimented with various species and everywhere ascertained 

 the perception of odours. I would recommend for such experi- 

 ments a species oi Erigone {E. rufipes^ Linn.), which, in this 

 country even in winter, may be everywhere shaken out of 

 firs and those shrubs which retain their dried leaves. This 



