Messrs. Hancock and Einblcton on the Anatomy o/Eolis. 193 



motion of the water they curl up their foot and fall to the 

 bottom. 



The oral tentacles, which are kept in perpetual action, seem 

 to possess the sense of touch in an exquisite degree ; so much so 

 that we are led to conclude, that from this circumstance, and 

 from their anterior position, they ought to be regarded as special 

 organs of touch. 



Taste, if present, most probably resides in the lining mem- 

 brane of the buccal cavity, particularly in the folds at the back 

 of the tongue (1st paper, PL I. fig. 8 h) and the cheek-mass, ef, 

 and perhaps also in the laminae at the commencement of the 

 oesophagus. 



When describing the third pair of nerves, we stated that we 

 considered the dorsal tentacles to which these nerves pass to be 

 distributed, as the olfactory organs, and for this opinion we now 

 proceed to adduce reasons which appear to be sufficient. 



That these tentacles are special and very important organs, a 

 consideration of the internal anatomical arrangement of their 

 nervous element and of the peculiarities of their external form, 

 peculiarities susceptible of great variety, would seem to leave very 

 little doubt in the unprejudiced mind. 



First of all a large nerve, PL V. fig. 3, among the largest in 

 the body, comes ofi* from the front of the median cerebral gan- 

 glion j and secondly, this nerve, or more properly speaking, trac- 

 tus, has superadded to it at the base of the tentacle a well- 

 defined ganglionic swelling, e, of a size exactly proportioned to 

 the extent of complexity in the external form of the tentacle. 

 Thus in E. 'papillosa, in which the tentacle is smooth and in its 

 simplest form, the ganglion is considerably less than in E. core- 

 nata, PL VI. fig. 6, and E. Drummondi, in both of which the 

 tentacle has a surface of a far more complicated kind, being ren- 

 dered much more extensive by the adJition of numerous broad, 

 circular laminse ; the ganglion being in these two species, as be- 

 fore noticed, upwards of one-third the size of the lateral supra- 

 cesophageal ganglion itself, PL VI. fig. 1 e, and PL V. fig. 2 e. 



If further evidence be required to illustrate the importance 

 and special nature of these organs, we may go from the genus 

 Eolis to the other members of the family Eolidida, as for in- 

 stance to Eumenis marmorata, in which we find the laminae so 

 closely set as to conceal the whole shaft of the tentacle, and 

 moreover there exists a sheath at the base of the tentacle into 

 which it can be retracted at the will of the animal. A sheath 

 also exists in Doto, PL VI. fig. 7, into which the organ, though 

 simple in form, is completely retractile. The same is found like- 

 wise in Dendronotus arborescens, PL VI. figs. 8 & 9, in which the 

 tentacle is remarkable for highly developed laminse ; and here the 

 Ann. ^ Mag. N. Hist. Scr. 2. Vol. iii. 13 



