MR. A. HANCOCK ON THE ANATOMY OF DORIDOPSIS. 203 
Now, if we turn to the oral apparatus in Doris tuberculata, we find that directly in 
front of the anterior extremity of the buccal organ there projects into the channel of the 
mouth a transverse fleshy lamina, the inner lip; and in advance of this the oral channel 
terminates in the outer lip. It would seem that the ridge within the termination of the 
proboseis represents the anterior extremity of the buccal organ or buccal lip in Doris, 
and that the thickened margin surrounding the orifice of the proboscis is the homologue 
of the inner lip, the channel of the mouth in front of this point being enlarged and 
developed into the sheath or sac of the proboscis. The margin of the external opening (e) 
in the sheath corresponds to the outer lip in Doris. If, then, we are correct in assigning 
the function of taste to the anterior extremity of the proboseis, it may be fair to assume 
that it resides in the inner lip of Doris, a part which has already been pointed out as the 
probable seat of this sense*. This, of course, is not conclusive; for it may have happened 
that the function of the parts has changed. It is, however, satisfactory to be able to 
observe that in Eolis, a genus which is provided with cutting jaws, there is likewise a 
similar inner lip. 
Touch is probably specialized in the small tentacular points at the sides of the head. 
As these are exceedingly short, they can only be serviceable in ascertaining the quality 
of the surface of bodies over which the animal is moving, and thus to assist it in the 
selection of its food. 
The auditory capsules were not observed, though there is no reason to doubt their 
existence. 
Having now completed our examination of the anatomy of Doridopsis, organ by organ, 
it is quite clear that, with one exception, the internal structure agrees with the external 
eonformation in showing the close relation of these animals to Doris. Indeed there is 
n0 internal or external character, with the above remarkable exception, that would 
induce the systematist to separate generically these two forms, unless the deficiency of 
spicula in the skin or the peculiar character of the head and position of the external 
oral opening should be thought sufficient. No one could have surmised that, in an. 
animal with all the other parts arranged so completely on the type of Doris, the powerful 
muscular buccal organ, with the spiny prehensile tongue of that genus, should be turned 
into a delicate suctorial proboscis; nor, after having witnessed this fact, is it easy to 
comprehend how such an important change in the alimentary system should not have 
drawn along with it some necessary and extensive modification of the other structures in 
the general economy of the animal. | 
Surely the mode of sustentation in Doridopsis is very different from that of any other 
Nudibranch, It is true that in both Melibe and Tethys the tongue is equally deficient; 
nor is there any spiny prehensile organ of any sort, or jaws, the oral apparatus being 
reduced, as it were, in these two genera to a mere enlargement of the anterior extremity 
of the @sophagus, guarded in front by fleshy lips. The change in these cases is restrieted 
almost entirely to the suppression of the lingual organ. But in Doridopsis, in addition 
* atrophy of the tongue, the buceal bulb is itself modified, as we have seen, into a 
* Phil. Trans. 1852, p. 243. 
