No.1.] ZHE DEVELOPMENT OF BALANOGLOSSUS. 15 
apical plate. Sections show that the two lateral horns of the 
body-cavity have grown larger. 
The second and third pairs of body cavities were not ob- 
served in the living animal, but sections show their presence, 
and show them to have enlarged between this and the last 
stage.1 The posterior pair of the two begins at the level of 
the posterior band, and thence extends backwards; while the 
anterior pair lies just in front of the posterior band, and is 
smaller than the last pair. 
The changes that were inaugurated in the last stage con- 
tinue, and the larva assumes the form shown in Fig. 5, Pl. I. 
The decrease in size has continued, and more marked is the 
decrease in the cross-diameter, for the larva at this stage is 
almost as long as in the one before. 
Larvae in this stage were still caught in the surface net, 
although the individual from which the figure was drawn had 
been kept for twenty-four hours in an aquarium. 
The body walls have thickened, and the larva has become 
correspondingly more opaque. Brown pigment spots are scat- 
tered through the ectoderm, and are more conspicuous along 
the lines where the anterior band formerly took its course. 
This band is almost obliterated at this time, particularly diffi- 
cult to see in the live animal, but when the walls are made 
opaque by the killing fluids, the remains of the band can be 
made out. At the apex of the larva are two conspicuous eyes. 
Each is crescentic in shape, with the convexities turned towards 
one another. The anterior end of each crescent is swollen 
out into a knob, as shown in the figure. 
The constriction near the middle of the body and at the 
level of the mouth has deepened, separating an anterior egg- 
shaped probosis from a posterior portion or body proper. At 
the ventral part of the constriction the large mouth opens 
directly to the exterior. 
The region between the constriction and the circular band 
is of about the same length as before, but shows faint surface 
lines that correspond to the posterior border of the collar. The 
1 These were overlooked in the brief account given in an earlier paper. 
