Nowi.| THE DEVELOPMENT OF BALANOGLOSSUS. 43 
eye is cut across the bulb. The lumen in Fig. 45 is bounded 
in the bulb by cells with clear ends, and on the outermost 
end of each such cell is formed a darker awn-shaped point. 
A round nucleus is found in the pigmented end of each such 
cell. Owing to the tortuous canal or invagination of the eye, 
it will be seen that certain of the cells are inverted. Thus the 
clear cells that in an earlier stage appeared at the surface of 
the apical plate are now carried far within the tissue of the 
eye —into the bulb, and some of them are there inverted. 
Lastly, to dismiss the subject here, we have drawn in 
Fig. 46 the outlines of the apical plate of an older stage. At 
the surface a pair of holes appear, and an examination shows 
that the eyes have sunken farther beneath the surface ecto- 
derm. In later stages, when the larva has entered the sand, 
these openings then disappear. 
We may next study embryos that have reached the stage 
represented by Fig. 6, Pl. I. The ectoderm has become thicker, 
as may be seen in the cross-section shown by Fig. 48, drawn 
to the same scale as Fig. 41. Details in the structure of the 
ectoderm may be gathered from the edges of sections drawn 
in Figs. 49, 50 and 51. 
The absorption of the tentacles has gone farther. A portion 
of a longitudinal section of the proboscis is drawn in Fig. 47. 
It represents a portion of the wall near the base of the ten- 
tacles, and the darker areas mark the last traces of the absorbed 
tentacles. Beneath each of the hemispherical masses is found 
on the inner wall a curious cell with a distinct nucleus. There 
is one of these cells at each area, but sometimes a smaller cell 
is attached to the large cell, as in one of the cells figured. 
The interior of this peculiar cell is homogeneous, and not 
granular. In other larvae of this same age I have found 
similar cells, but in no one of the other larvae were these 
cells so large and conspicuous as in the one figured. I do 
not know the fate of these cells, and they may be pathological, 
but this would hardly explain their constant position in con- 
nection with the tentacles. It is of course suggested from 
their position that they have something to do with the absorp- 
