146 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



parts they are, on the contrary, very rare or absent. Sense- 

 cells in the central part of the body are likely to serve some 

 other purpose. 



We have seen that Oligochseta possess cells perceptive of 

 light, taste, smell, and touch, and unless we assume the 

 existence of a sixth sense not present in the higher animals, 

 the only remaining sense not yet fully recognized in Oligo- 

 chaeta is that of hearing. The nature of the structure of 

 the sense-cells in Pontoscolex and Eiidrilus is such as not 

 to oppose the assumption that in these cells may be recog- 

 nized primitive auditory organs. In Pontoscolex the char- 

 acteristic parts of the auditory cell are the otosome and the 

 diaphragm. In Eudrilus the diaphragm only is present, 

 but it does not seem improbable that the almost vertical 

 column of nuclei superposed on the large lower cell may 

 serve as a row of otosomes, aiding materially in carrying 

 along the sound-waves to the diaphragm of the more sensi- 

 tive cell below. It is of the utmost importance that the worms 

 be enabled to perceive sounds caused by the feet of 

 birds, the working of moles and other animals, — sounds 

 which must be transmitted through the soil in order to reach 

 the worms. 



The situation of the sense-corpuscles in the projecting 

 equatorial of each of the more central somites in those parts 

 of the body which come into closest contact with the soil, 

 seems to me to especially favor the theory that these cells 

 and corpuscles are really organs for the perception of 

 sound. Not only are these cells more numerous in the 

 equatorial of the central somites, but they are nearly exclu- 

 sively found on the dorsal and lateral sides of each somitic 

 equatorial, and are almost absent on the ventral side. In 

 other words, they are most numerous^in parts most access- 

 ible to sound-waves passing through the soil, and are singu- 

 larly scarce in parts which are least accessible to these 

 sound-waves. These cells in Eudrilus Eugemce, as well 

 as in Pontoscolex, are found several rows abreast in each 

 equatorial, and are never found outside of the equatorial. 



