Chap. XII.] 



ORGANS OF TASTE. 



435 



considering ; these, which are most numerous on the 

 cirri and in the neighbourhood of the mouth, lie side 

 by side with the ordinary epithelial cells, from which 

 they are to be distinguished by a stiff free process, and 

 a basal connection with a nerve fibre, calling to mind 

 again the simple sense cells of the Medusae. A very 

 ordinary character of tactile cells among the 

 Verteforata is their bulb-like arrangement (see 

 " Elements of 

 Histology," chap, 

 xv.) ; they are, 

 as may be sup- 

 posed, widely dis- 

 tributed over the 

 whole body, al- 

 though, of course, 

 they are much 

 more richly de- 

 veloped in some 



Fig. 186. Tactile Organ of Sagitta bipunctata, 

 showing the long stiff setae. (After O. 

 Hertwig.) 



in 



parts than 

 others, and in 

 some forms more 

 than in others. 



Organs of taste. Although we may well 

 suppose that some sense of taste is possessed by the 

 lower Metazoa, we have as yet very little definite 

 information as to organs to which it is reasonable to 

 ascribe such a function. In the Echinoidea (ex- 

 cepting Cidaris) Loven has described, under the name 

 of sphseridia* organs to which he assigns a 

 gustatory function. These are always set around 

 and confined to the region of the mouth (actinostome), 

 where they have the general appearance of transparent 

 solid bodies invested by pigmented cells and a 

 ciliated epithelial layer. Just as the auditory organs 

 of some Ccelenterates appear to be modified tentacles, 

 so do the sphseridia remind us in the most striking 



