No.1.] ZHE DEVELOPMENT OF BALANOGLOSSUS. 53 
A figure from a horizontal section of an embryo is drawn in 
Fig. 70, to the same scale as the surface view of this stage. 
(See Fig. 8, Pl. II.) In the upper portion of the figure the 
collar is cut. Its interior is filled by the collar-cavity into 
which the collar-pores open at the sides. The interior of the 
body-cavity is filled with scattered muscle (or mesenchyme- 
like) cells not seen in the figure. Behind the collar the section 
passes through the upper portion of the gill-region. Portions 
of the tongue-bars and dividing-bars are found on each side. 
Into both tongue-bars and dividing or between-bars the pro- 
longations from the third pair of body-cavities are found 
almost completely filling up the interior. The outer surface 
of the between-bars is, of course, ectodermal, but the outer 
exposed surface of the tongue-bars is endodermal. 
The digestive tract is thrown into folds and its whole outer 
surface is covered closely by the splanchnic layer of the body- 
cavity. The walls of the digestive tract get thinner as they 
extend posteriorly. 
From the same series we gather that the eyes have not 
entirely disappeared. Brown pigment, surrounding a few clear 
cells, mark their position. 
The second and third body-cavities are filled by delicate 
fibre-like cells (not seen in the figure). These are most abun- 
dant at the posterior end of the third pair, when the body 
swells up into a bulb, and they connect the somatic and 
splanchnic walls. 
The muscle-fibres of the walls are entirely longitudinal in 
both the second and third pairs of body-cavities. A double- 
walled septum separates these two cavities from one another. 
A figure of the nervous system, taken from a larva, either 
just at this stage or a little prior to it, is shown in Fig. 71. It 
was obtained by opening the collar and removing the nervous 
system along with the collar. The preparation is looked at 
from within. The length of the nerve cord is shown by the 
bar of. tissue running from one end of the collar to the other. 
For comparison there is placed alongside of this figure another, 
shown in Fig. 72,—-a similar preparation from a larva at 
Stage 6. In the latter figure the bar is exceedingly short 
