222 Proceedings of the Royal Society of Victoria. 



epidermic cells are much elongated to form tactile cells (T), with 

 their nuclei placed at thieir inner ends. A nerve, arising in some 

 oases directly from the supracesophageal ganglion, in others as 

 a branch of the optic nerve, passes up, giving otf branches which 

 supply two or more organs lying next to one another, so that the 

 dififerent sense organs are not necessarily supplied with differently 

 functional nerves. The tibres enter the inner end of the groups 

 of tactile cells and are distributed to them. I have noticed, in 

 some sections, one or two large clear cells (c.c.) placed on the 

 nerve fibres, the function of which I am unable to explain. As in 

 the case of the other sense organs these on the margin of the lip 

 are well supplied with blood by means of small vessels passing 

 up between the ordinary epidermic cells and giving off branches 

 which pass round the organ and supply it on all sides (Bv). 



In respect to time of origin Whitman says that the segmental 

 .sense organs have been developed first, for the others — the 

 non-segmental — are limited to a specialised part of the animal 

 and have undoubtedly arisen in response to the increased needs 

 of this part. 



The functions of these various sense organs have been fully 

 discussed by Whitman.^ Undoubtedly the marginal lip organs 

 subserve the sense of touch and may possibly serve as organs of 

 smell. 



The exact way in which the eyes function as organs of sight 

 is yet to be decided. At least they can appreciate light and 

 <larkness. Owing to the fact that the segmental sense organs 

 and the eyes both possess large clear cells — these being most 

 numerous in the latter — Whitman concludes that both classes of 

 organs have a common function, namely, the appreciation of 

 light and darkness. It is also probable that the segmental sense 

 ortrans act as ormms of the sense of smell. 



Ali/nentaty Canal. (Figs. C, 4 and 9-19). 



The alimentai-y canal of Philremon resembles that of Hiriido 

 mediciiialis in many respects. It opens on the ventral surface at 

 the anterior end by the anterior sucker and extends back along 



1 Q.J. M.S., vol. xxvi., p. 408. 



