No.1.) ZHE DEVELOPMENT OF BALANOGLOSSUS. 33 
the nuclei are more abundant and stain more deeply than else- 
where, but are somewhat smaller. A cross-section of one of 
the tentacles is shown in Fig. 18. The ciliated band, cut 
twice, appears on the outer sides of the tentacle. Its nuclei 
are more abundant than the other nuclei of the section, and 
the ectoderm of the band is much thicker than that over the 
rest of the body. The tentacle contains a central space that 
is merely an extension of the blastocoel space. 
A view of the apical plate is shown in Fig. 19. In the cen- 
ter of the plate is a clear area, oval in outline, with conspicu- 
ous nuclei. The structure is best brought out by staining in 
Haematoxyln, but may readily be seen in unstained prepara- 
tions. A small portion of a cross-section of this region is 
shown in Fig. 22, in the upper left corner of the figure. Here 
the ectodermal nuclei are seen to be less abundant, and the 
cells vacuolated to a very great extent. Beneath, an irregular 
layer of larger, more rounded nuclei separates the clear vacuo- 
lated portion from the punctated layer. To the center of this 
structure is attached, on the inner surface, the muscular wall 
of the proboscis body-cavity. I have no conception of any 
particular function that this organ may possess. 
On each side of this body lie the two crescentic eyes, with 
knobbed anterior ends (Fig. 19). A dark-brown pigment is 
present in the eyes. The ectoderm around the eyes is also 
faintly marked by finely granular pigment. 
Four ciliated bands end in the plate. The anterior pair 
run almost to the knobs of the eyes. The termination of the 
band is in stained specimens definitely made out; in fact the 
very last nucleus of the band is easily separated from the sur- 
rounding nuclei of the apical plate. The rest of the apical 
plate is covered by ectoderm rich in nuclei as seen both in 
surface views and sections. Under the apical plate the punc- 
tated layer is thicker than elsewhere more especially along the 
gutters between the parallel lines of the ciliated band. In 
the ectoderm outside of the bands clear areas are found sur- 
sounded by nuclei. Each probably corresponds to a gland. 
On account of the large size of the eyes I have been able to 
make out their structure somewhat in detail. A surface view 
