408 Cc. O. WHITMAN. 
their special function is more or less intimately associated with 
the work performed by the eyes. Although I do not feel 
prepared to adopt without reserve the opinion that they 
represent simply a dioptric mechanism, I think their presence 
in the eyes and the segmental sense-organs furnishes good 
ground for thinking that both classes of organs have a common 
function. Add to this their serial homology and the evidence 
becomes stronger in favour of the view maintained in this 
memoir respecting the function of the segmental sense-organs. 
But how are we to explain the presence of the same large 
clear cells along the nerve-branches running to the goblet- 
shaped organs of the lip? They are not here associated with 
the peripheral sensory cells, as they are in the eyes and the 
segmental sense-organs, and I am not certain that they are 
constant. All that I can say is that they are to be seen in 
some of my sections of the Land Leech, and I confess to being 
quite unable to offer any explanation of them in this position. 
While still maintaining that the segmental sense-organs, as 
well as the non-segmental sense-bulbs scattered over the upper 
surface of the head, share in the work of the eyes, I am 
strongly inclined to think that this is not their only work. In 
the case of the Land Leech I have obtained some evidence of a 
sense of smell. A breath thrown into the bottle containing 
these Leeches instantly puts them into a state of very great 
excitement. They move about in great haste, as if aware of 
the presence of some object tempting to their appetite. Any 
jar of the bottle is sufficient to excite them, but disturbance of 
this kind, however violent, falls far short of giving the stimulus 
imparted by a gentle breath. In removing specimens from one 
bottle to another I have often found a few of the less hungry 
ones disinclined to accept any opportunity to leave the bottom 
of the bottle. In such cases, when all other expedients failed 
to bring them out, I have found that breathing upon them 
soon induced them to come to the mouth of the bottle. 
My observations on the habits of Clepsine marginata 
were made before my attention was directed to the question 
here considered; but, so far as my recollection serves me, I 
