Olfactory Organs of Spiders. 333 



us one or two rows, as the hairs then are alternately larger 

 and smaller. 



The rudimentary cups upon the tarsus are usually of about 

 the form shown in fig. 3. The connexion with the internal 

 space is here completely cancelled. Sometimes also the 

 upper surface is almost entirely closed, so that then there 

 remains only a vesicle in the integument. Moreover, the 

 hair on the metatarsus in many cases shows only a small 

 amount of mobility, far inferior to that of the tibial hairs. 

 Perhaps in time this hair also will meet with the same fate as 

 the hair of the tarsus. 



After the appearance of my communication in the ' Zoolo- 

 gischer Anzeiger ' I was for a time in doubt whether the 

 sound-waves were i\iQsole adequate excitation for the auditory 

 hairs. The ground of this doubt was furnished by the con- 

 sideration, which was even then indicated, that the hairs are 

 also fitted to convey the sensation of a puff of air. Thus, if 

 one blows upon a Lycosid, for example, when it is slowly 

 running along or resting quietly, it draws up the legs to the 

 body. As it decidedly does this involuntarily, and there can 

 be no question of an actual fright of the spider, I thought 

 that we must recognize in this an instinctive protective 

 arrangement of some kind. Perhaps the animal would 

 instinctively hold fast, and at the same time present to the 

 wind as small a surface as possible. But if I only blew as 

 strongly as would occur at the utmost in the wind, I observed 

 scarcely any shrinking. The strong and sudden shock of the 

 wind would therefore have to be a painful over-excitation of 

 the organ, and the shrinking a sign of pain. Bat if the hairs 

 really serve for the perception of a breath of air, we must at 

 the same time ascribe to them the other function of sound- 

 perception, as we are compelled to assume that every move- 

 ment which is directly conveyed to tiie termination of a nerve 

 is felt ; and that the sound-waves set the hairs in motion may 

 be directly observed, as has been previously stated. 



The organ which I characterize as the olfactory organ is 

 represented in figs. 4-6. Fig. 4 shows a section through the 

 maxilla in the direction of the length of the body. In this 

 vid indicates the section of the maxillary gland * and m a 

 muscle in section, both enclosed in coiniective tissue ; go is 

 the smooth anterior surface in fi'ont of which the mandibles 

 move to and fro. This smooth hairless ar(;a on the anterior 



* ' Analytisfhe Be.'irbfitiiug,' kc. p. 18, ivsp. 0. 

 Ann. cJt; Mag. N. Hist. Ser. 5. I'o/. xiv. 26 



