194. Messrs. Hancock and Embleton on the Anatomy of Eolis. 
sheath, which is long, and into which the tentacle is quite retrae- 
tile, is garnished around its extremity by a circle of arborescent 
filaments, by which the organ even, when extended, is to a_ 
great degree protected from injurious contact with surrounding 
objects. 
otra as if the laminated disposition of the tentacle were not 
sufficient for the purpose of the Antiopa splendida, Pl. V1. fig. 10, 
we have these organs, aa, standing out from the sides of a me- 
dian crest, b, which is elevated above the surrounding skin, and 
crowned by a series of pinnate laminze. That this median crest 
is really a part of the olfactory organ, an addition to its com- 
plexity, is proved by the attendant modification of the nervous 
element, which is as follows. There is directly in front of and 
in contact with the median cerebral a pair of small ganglia, ce, 
each of which gives off two branches, one of which, d, goes to ~ 
the tentacle, and the other, e, much thicker, goes to one half of 
the median crest. 
We could easily adduce other examples from the Dovid 
if others were required, to show the importance and the spe- 
ciality of these organs ‘in the Nudibranchiata, but those we have 
brought forward seem enough for this purpose. Another cir- 
cumstance bearing upon the special nature of these tentacles, 
and noticed by Joshua Alder, Esq., one of the authors of this 
paper, in a communication made to the British Association 
at the Cork meeting, is that the cilia on their surface vibrate in 
a direction contrary to that of those on the surface of the © 
branchial papille. On these the cilia move constantly from the 
body towards the extremity of the papilla; on those they act from 
the point of the tentacle towards the body ; thus, im the former 
case, the water which has served for respiration is drawn from 
the body and thrown off from the apices of the papille, whilst in 
the latter the fluid which we may suppose to contain odorous 
particles or qualities is attracted to the end of the tentacle, and 
made to pass down over the entire surface, and then thus to act 
upon the sentient nerve within. 
Now it is a constant occurrence in the higher animals that the 
fluid to be tested by the olfactory organ is always brought to the 
nerve, and made to pass over the sensitive surface in the majo- 
rity of instances by means of the agency of inspiration. In fishes 
however in which the nasal cavity is shut off from the mouth and 
throat, another agency than that of respiration is required; the 
olfactory plates however are freely supplied with cilia, and these 
probably act a part analogous to those of the laminated tentacles 
of Eolis. But the dorsal tentacles are not only, according to our 
view, important and special organs, but they are, further, organs 
of smell. Their laminated structure is one evidence of this, The 
