396 
E. RAY LANKESTER. 
Balanoglossus, are fused to the body wall immediately behind 
the mouth. In front of this region they project as an almost 
complete collai’, the so-called prseoral hood ; behind it they 
are not short and annular in direction, as in the posterior 
collar of Balanoglossus, but are extended horizontally so as to 
enclose the whole perforate region, and their free margins fuse 
together below the ventral wall of the pharynx. Still we can 
easily imagine a reduction of the epipleural folds of Amphi- 
oxus which would give us them in the form of an incompletely 
annular fold, overhanging only the three or four anterior gill- 
slits. Now, if we consider the position of the atrio-ccelomic 
funnels, we find that they are in the base of the epipleural 
folds, and therefore, with the reduction and shrinking of the 
epipleura, would come to lie very much in the position occupied 
by the collar-pores of Balanoglossus. 
Whether the atrio-coelomic funnels of Amphioxus, the 
collar-pores of Balanoglossus, and the abdominal pores of 
Craniata are to be considered as modified nephridia, is a 
question upon which I am not prepared to enter. Our con- 
ception of the nephridium as a unit of structure common to all 
Coelomata, is at the present moment undergoing development 
and extension. But whilst we now refer to this category the 
genital ducts of Arthropoda and Mollusca, as well as glandular 
tubes with excretory functions, and whilst our notions as to 
the limitation of the number of nephridia in one individual or 
one segment are greatly modified, we must be careful not to 
assume too hastily that every opening in the body wall of a 
coelomate animal communicating with its coelom, is neces- 
sarily the opening of a nephridium. It is not impossible 
that so wide a generalisation as this may be established, but 
in the meanwhile it seems possible to distinguish such aper- 
tures as the dorsal pores of Lumbricus from nephridial 
openings, and so long as the former are not shown to be 
related by origin to nephridia, it will be necessary to admit 
the existence of a category of pores which have not, and never 
had, any relation to “ a specialised tubular portion of coelom, 
the lining cells of which have an excretory function.” The 
