594 
(STÖHR, 1890); (3) that the cells which reticulate the epithelium and 
epithelial downgrowths are derived, not from the vascular channels, 
but develope in situ from the connective tissue (mesenchymal) elements 
(HAMMAR, 1903). It may, perhaps, be pointed out that the greatest 
common factor of all three views is the recognition of epithelial 
downgrowths which disappear as such by a process of transformation 
or absorption effecting also the surface epithelium, — which while 
it is little understood as yet 1s obviously connected with the develop- 
ment of tonsillar structures. The problem is one of double character 
or phase, being first a part of the problem of lymphatic tissue in gene- 
ral, and secondly, the problem of the tonsils proper, including, there- 
fore, location and the peculiar relations to epithelium and other 
structures. 
In the development of the palatine tonsil of mammals, while 
the work of Hıs and Hammar particularly has shown that it developes 
at the site of the second visceral pouch, whatever morphogenetic 
significance attaches to this association in development remains ob- 
scure. Two points stand out: (a) the relatively late development 
of the tonsil, a considerable period intervening between the disappear- 
ance of the branchial pouch as such and the appearance of the ton- 
sillar lymphatic tissue; (b) the peculiar histogenetic relation of the 
tonsil to epithelium and epithelial structures above referred to. The 
morphogenesis of the other mammalian tonsils is still insufficiently 
worked out. 
The existence of tonsil-like structures in the Amphibia had been 
known to the writer for some time. When therefore time and faci- 
litiest) for their adequate examination presented themselves, it was 
undertaken in the hope that the development in these simpler forms 
would throw some light upon the morphogenetic factors operative 
in the development of the tonsils in higher forms. It may be said 
at the outset, however, that such expectations have been only in part 
justified. 
1) This study was begun in the “Histologisch-Embryologisches Institut” 
at Miinchen. The supply of Salamandra atra material placed at my disposal 
was lavish and generous. I desire to take this opportunity of acknowledging 
the interest and help accorded to me by Professor MoLLıer, Director of the 
Institut, and by the late Prosektor, Dr. ALEx. Bonum. To Professor 8. H. Gace 
of Cornell University, I am indepted for suggestions and for assistance in the 
illustrations. 

