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been done upon the development of the lymphatic nodules along the 
digestive tract indicates that, — as has of course been recognized, — 
there is no fundamental distinction to be drawn between tonsils and 
other collections of lymphatic tissue occurring in or under the mucous 
membrane of the digestive or respiratory tracts. A general discussion 
of this phase of the subject is, however, not within the scope of this 
paper. 
The application of the term ‘‘tonsil”’ to these structures in Am- 
phibia is thus in accordance with the characteristic structural features 
possessed by them in mammals. The structural relations are here the 
simplest. The mass of small cells is simple, — several distinct centres 
of proliferation (nodules) are absent or at least not demonstrable. 
The involvement of the epithelium is typical. The source of the small 
cells remains here as elsewhere, — in man and mammals, — a crucial 
point in the analysis of their structure. Any consideration of the 
histogenesis of the Amphibian tonsils has, however, been purposely 
avoided in the present paper, as it is hoped to take that phase of the 
subject up specifically at some future time. 
While the number of inviduals and forms has not been large, 
it is enough to show clearly that a considerable variability underlies 
the appearance and location of the tonsillar patches in Amphibia. 
This variability, however, is not absolute, since in certain regions 
notably in the case of the lateral, sublingual, preglottideal and choanal 
tonsils, they occupy morphologically constant places, which in the 
case of three of these at least, mark points of epithelial obliteration — 
at the time of metamorphosis. These facts indicate clearly, it seems 
to the writer, that the factors which determine the appearance of a 
tonsillar patch at any particular point are not intrinsic, — in the cells 
that make up the tonsillar structure. In other words, no cells, either 
in the connective tissue or epithelium are destined, — predeter- 
mined, — to form a tonsil, but that the morphogenetic factors are 
extrinsic; that is, the tonsils appear where and when they do as a result 
of certain conditions of interrelation, which may or may not prevail 
and lead to tonsil formation. 
As an element in the tonsil-determining factors appears to be 
regressive change such as occurs in the disappearance of structure in 
metamorphosis. Whether the changes in the epithelium are pri- 
marily more important, or whether the connective tissue cells have 
an initiatory influence, or whether a vascular element enters into the 

