ORIGIN—_TASTE-BUDS OF ELASMOBRANCHS 53 
that by a process of substitution this endodermal lining is second- 
arily replaced by ectoderm has never been given. The demon- 
stration of an ectodermal dental ridge cannot be considered to 
be a demonstration of an ectodermal lining of the pharynx. 
It is equally fallacious to conclude that because annelids have 
an ectodermal foregut vertebrates must have an ectodermal 
pharynx. On the contrary, direct observation proves that the 
lining of the pharynx of vertebrate embryos is entodermal in 
origin. 
3. “The presumption, from the standpoint of nerve distri- 
bution, is all in favor of the origin of taste-buds from endoderm”’ 
(Johnston, 10, pp. 64, 65), since they are ‘‘innervated by the 
facial nerve which is strictly a nerve related to entodermal sur- 
faces in all vertebrates except those fishes in which the taste- 
buds spread into the outer skin.”’ 
CONCLUSIONS 
1. Taste-buds in Squalus acanthias are limited to the pharynx, 
where they are distributed over the floor, the roof, and the gill 
pouches. 
2. The structure of the taste-buds resembles that of taste- 
buds in other forms. They are groups of slender cells slightly 
raised above the surface into a papilla. Each cell bears, exter- 
nally, a hair-like process, and is connected internally with a nerve 
ending. 
3. Taste-buds in S. acanthias are derived from the endoderm. 
They develop from the epithelial lining of the pharynx which at 
all stages shows itself as endodermal, there being no indication 
at any period of development of a migration inward of the ecto- 
derm, except the slight invagination which forms the dental 
ridge. 
4. The pharyngeal scales arise in late embryonic stages. They 
resemble placoid scales in structure, but are derived from the 
endodermal lining of the pharynx. 
