Affinities of the Sponges. 87 
difference of the function of common parts, and has no homo- 
logical import. No one thinks of separating certain oligochzet 
worms, such as ZEolosoma, which take in their food by ciliary 
action, from the others which use a powerfully developed suc- 
torial pharynx; nor of detaching the Chætopods with pre- 
hensile jaws in their pharynges from those which have none. 
Mr. Kent’s statements with regard to the voluntary action of 
muscular tissue and the involuntary action of cilia, and the 
consequent psychical distinction between sponges and corals, 
are worthy of remark, because, in the first place, if the distinc- 
tion be allowed, we have to admit a totally novel differen- 
tiating character. Mr. Kent ventures to say that Hückel asso- 
ciates sponges with corals by looking to analogical rather than 
homological affinities,—and then actually proposes to distin- 
guish them by psychical manifestations. Can any thing be 
further from homological argument than that which he here 
uses? Moreover the voluntary nature of muscular action 
and the involuntary nature of ciliary action cannot be admitted 
on any terms. It is useless to import the term “ voluntary ” 
into the discussion ; but it is true that where a nervous system 
* In another paper (p. 34) I have discussed the signification of the term 
homology in evolutional zoology, and have proposed to replace it by the 
term is komioying in the particular sense which is above implied. 
