Nout.) ZHE DEVELOPMENT OF BALANOGLOSSTS. 23 
to the exterior and each is partially divided by a tongue bar 
projecting into it from the dorsal wall. Each slit is relatively 
larger than in the preceding stage. The slits may be en- 
tirely exposed on the upper surface or may be partially over- 
arched by two lateral folds of the body wall. An attempt is 
made in the figure to show the position of these folds when 
the gill-slits are exposed. A constriction separates the oesoph- 
agus from the stomach-intestine. The large tube-like digestive 
tract runs the whole length of the body, opening at the 
posterior end by a large anus. In the anterior region — in 
front of the plane of the circular band —the walls of the 
digestive tract are thrown more into folds than in the region 
behind the band. This anterior region represents the hepatic- 
region of the young worm. 
The posterior region shows the same bulb-like swelling of 
the earlier stages. 
The oldest stage that is drawn /o the same scale as the pre- 
ceding’ stages is given in: Fig, 10, Pl. Hl, caught, June.24, 
killed July 5. The general enlargement of the body is obvious 
and the relative sizes of the organs at the anterior end have 
changed greatly as compared with earlier stages. The probos- 
cis has become more pointed and is of about the same length 
as in the last stage. Its cross-diameter is much smaller. The 
collar has increased a good deal in size. 
In the region of the body behind the collar the circular 
band of pigment may still be found, but is much more irregular 
than heretofore. The relative proportions of the body before 
and behind the band are the same as in earlier stages. 
The gill-slt region covers a greater area than before and 
each gill-slit has increased in size. Five or six pairs of these 
open at the surface, while a smaller pouch that has not yet 
reached the surface could be seen. Only three pairs were seen 
in the living worm. The gill-bars are large and conspicuous. 
The outline of the digestive tract may be seen through the 
body walls. Behind the gill-slit region the oesophagus narrows. 
The next portion of the tube shows an irregular series of con- 
strictions or slight pouches. At this time this region of the 
