THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 45 
intervenes between the appearance of the placode and the 
appearance of the taste-buds in Lepidosteus than in Amelurus, 
which is the slower growing form. Of more significance still, 
is the relative number of taste buds present at a stage when 
both types have them developed fully enough so that they can 
be counted with certainty. Two series fulfil these conditions 
closely, Lepidosteus at 214 hours and Ameiurus at 213. At the 
age of 214 hours, Lepidosteus has 32 taste buds distributed on the 
roof of the oral cavity and pharynx, and on all five gills. Owing 
to the large number of mucous glands on the outer surface of the 
body and the presence of the adhesive disc on the head where 
external buds are most likely to be found, it is not possible to 
determine the number in the skin. 
In Ameiurus at 213 hours there are 146 taste buds in the oral 
cavity, 352 in the pharynx and gills and 117 situated externally 
on the skin of the head chiefly. This gives a total of 615 taste 
buds in Ameiurus as compared with 32 for Lepidosteus for a 
corresponding age. The later appearance and slower rate of 
growth of ganglia and limited number of taste buds in Lepidos- 
teus as compared with Ameiurus of the same age seem to offer, 
when we consider the different rate of growth in the two types, 
strong evidence that the gustatory system of Lepidosteus is 
retarded in development as compared with other structures in this 
form and that this retardation is indicated in the histological 
differences between placodal and neural crest cells and offers a 
satisfactory explanation of the retarded metamorphosis of the 
special visceral cells into normal ganglion cells. 
5. The assumption that cells derived from the epibranchial 
placodes, after their metamorphosis into ganglion cells, are the 
cells giving rise to fibers supplying taste buds and consequently 
designated as special visceral ganglia, rests upon indirect evidence 
but evidence of such a character as to warrant the assumption 
in view of the extreme difficulty of demonstrating its truth or 
falsity. Epibranchial placodes are found in all types of verte- 
brates, even among mammals, including man. Among the lower 
vertebrates where their history can be followed in series taken 
at close intervals, they can be shown in some cases to con- 
