336 On the Auditory and Olfactory Organs of Spiders. 



animal not only reacts very easily, but it is also particularly 

 well adapted for the experiments on account of its behaviour. 

 If it be placed in a covered vessel it will soon sit quietly on 

 the wall with its legs drawn up to its body. In this position 

 it is not easily disturbed. But if a brush dipped in oil of 

 turpentine or oil of cloves be brought within half a centi- 

 metre (i inch) of it, it regularly runs away in a few seconds. 

 I have not been able to observe any difference of behaviour 

 towards different odours, nor could I succeed from its actions 

 in drawing any conclusion as to the position of the olfactory 

 organ, the animal being too small to allow experiments to 

 be made with this object. This, however, is certain, that 

 spiders perceive odours ; and as we find no corresponding 

 organ in the neighbourhood of the organs of respiration, tlie 

 conclusion that the organ described is actually an organ of 

 smell may appear not inadmissible. 



A priori it would seem useless to seek for histological 

 analogies, seeing that in other Arthropods we have no more 

 certain knowledge as to the olfactory organ ; and a comparison 

 with the corresponding organ in Vertebrata, which are con- 

 structed upon quite a different type, does not seem to be 

 permissible. Hence we are only the more surprised that an 

 analogy with the structure of those animals, as it were, forces 

 itself upon us. The olfactory cells, in fact, very vividly re- 

 mind us of the so-called epitlielial cells in the olfactory 

 mucous membrane of the Vertebrata. It is true that here 

 precisely that is wanting which we there interpret as olfactory 

 cells. This interpretation, however, is still scarcely to be 

 regarded as demonstrated, especially as the so-called olfactory 

 cells sometimes bear vibratile cilia, and therefore at the same 

 time must serve another purpose. The subepithelial layer 

 would represent the membranous plate, which here certainly 

 does not appear to consist of cells. 



In this place I may perhaps call attention to another pecu- 

 liar organ of the Spiders. I call it an organ on account of 

 its peculiar structure and its general diffusion, although I can 

 say nothing as to its function. It occurs upon the upper 

 surface of the metatarsus of all the legs towards the extremity, 

 and consists, as shown in fig. 7, of a few transverse folds, 

 some of which show dot-like enlargements. In some Thera- 

 phosidaj the outermost fold is even closely and uniformly 

 toothed on the margins. In longitudinal sections there ap- 

 pears under these folds (fig. 8) an oval, clearer mass of the 

 matrix, which is surrounded by pigment-grains and might 

 remind one of a nerve-termination. Hitherto, however, I 

 have not seen any nerve-fibre running to it. Does this organ 



