62 J. B. Johnston. 
ules are closely packed around and among the nuclei of the cells 
which form the sense organ. It presents the same appearance as do 
early taste buds in the roof of the pharynx or in any part of the 
mouth, whether near the ectoderm or far from it. 
Another taste bud in a shghtly later stage of development is shown 
in Fig. 20. It is situated in the roof of the mouth just behind the 
most lateral one of the vomerine teeth. The cells immediately around 
the tooth together with the three or four deep nuclei at the right hand 
end of the figure (asterisk) come from the ectoderm of the dental 
ridge. All the rest of the cells are entoderm. At the left, several nuclei 
vertically arranged indicate the beginning of a taste bud. It contains 
Fic. 20. A. punctatum after the formation of the mouth cleft. Sagittal 
section of the roof of the mouth in the vomerine region. At the left is a taste 
bud forming. At the right the asterisk marks the border of the ectoderm. 
Iron hematoxylin, fuchsin. 
and is surrounded on all sides by large yolk granules such as are found 
in this embryo only in entoderm and in parts of the mesoderm. 
The ectoderm has no yolk at all in embryos of this stage and the 
nervous system has very little. 
In Fig. 21 are shown three taste buds and one neuromast from a 
larva four or five days after the formation of the mouth opening. 
The entoderm is still clearly distinguishable from the ectoderm and 
extends beyond the teeth to the lips. At A in the figure is a taste bud 
standing near the vomerine teeth. The deep nuclei which show active 
nuclear changes belong to the ectoderm of the vomerine dental 
ridge. The two cells with dark nuclei belong to the mesenchyme. 
These cells and the definite outline of the entoderm show that there 
