AHPHIOXTJS LANCEOLATUS. 
395 
vertical plane passing through the narrower part of the atrio- 
ccelomic funnels will also cut the deepest and most fully deve- 
loped region of the perforations of the pharynx as shown in 
PI. XXXVI. 
I am not able to offer any suggestion as to the function 
of the atrio-coelomic funnels, based on positive characters. 
Their inner cell-lining appears not to be glandular, and their 
connective-tissue tunicis equally devoid of any special characters. 
It is possible that they may serve either to admit water to the 
coelom or to remove the coelomic liquid under conditions of 
tension. The structure and position of one of these funnels 
render it probable that were there greater tension of liquid in 
the coelom than in the atrium its walls would be pressed together 
and the funnel closed. On the other hand, were there greater 
tension of the sea-water contained in the atrium than of the 
coelomic fluid, the funnel would be dilated and sea-water would 
flow into the coelom until the tension was equalised. 
Morphologically, the atrio-coelomic funnels are paired short 
tubes placing the coelom in continuity with the exterior, for 
the atrial cavity is morphologically external surface. In so 
far they correspond with the abdominal pores of craniate Verte- 
brata. Mr. Bateson (2) has shown that they have a remarkable 
correspondence in other respects to the collar-pores of Balano- 
glossus. The collar of Balanoglossus is, like the epipleura of 
Amphioxus, an outgrowth of the body wall. It may be com- 
pared to a dice-box open at each end and fused with the body 
wall of the Balanoglossus (over the head of which it has been 
pushed) all round the inner surface of its constricted middle 
third. It is thus in fact not one collar but two, one having its 
free circular margin directed forward and the other having its 
free circular margin directed backwards. The anterior collar 
surrounds and conceals the mouth and the base of the pro- 
boscis ; the posterior collar surrounds the commencement of 
the pharyngeal perforated region and overhangs two or three 
gill- slits. It is on the under surface of this posterior collar 
that the pair of collar-pores are placed. 
The epipleura of Amphioxus, like the double collar of 
