Novi] 22 DEVELOPMENT OF ._BALANOGLOSSUS. 49 
as we shall see, do in later stages meet above the cavity to 
form the dorsal wall of the tube. 
Other minor points may be recorded. 
The eyes are still present, but show signs of degeneration. 
A small central tube seems still to open at the surface. 
The large circular ciliated band is disappearing. Sections 
show that its large ciliated cells are breaking down. Irregular 
pieces of these lie scattered along the former course of the 
band. These pieces show distinct striations resembling muscle 
cells. Not only are these pieces to be found along the course 
of the band, but they can be clearly recognized in the ectoderm 
some little distance away from their previous position. How 
it was possible for these pieces to be carried through the thick 
mass of ectodermal cells I do not know, but there cannot be 
the least doubt of the fact. 
The small posterior ciliated (circular) band is also to be 
found at this stage. The ectodermal cells lying along the 
mid-dorsal line of the trunk behind the collar become smaller 
and stain differently from the other cells of the ectoderm. 
The ectoderm of the collar is quite thick, and a distinct 
circular groove marks the posterior limit of this region. 
Surface views of the inner side of the collar show the plate 
of ectoderm forming the nerve-chord. It is slightly longer 
than broad, as shown in Fig. 72, Pl. VI, and is continuous 
both in front of and behind the collar with the surface ecto- 
derm. 
Surface preparations of the proboscis show that the areas of 
absorption of the tentacles may still be traced. It will be 
found that the anterior edge of the collar coincides with the 
horizontal limb of the anterior circular band, and that the small 
dip in the middle of the band runs over the surface of the 
collar. 
Dissections show that the oesophagus carries three pairs of 
gill-pouches that protrude from its upper (lateral) surface, and 
that the gill-pouches lie somewhat in a dorsal chamber of the 
oesophagus. 
The constriction between stomach and intestine can still be 
traced. 
