400 ANNALS NEW YORK ACADEMY OF SCIENCES 



The hypothetical common pro-mammalian gromid-plan of bronchial 

 architecture, from which all extant types are derived by modifications, 

 either in the direction of further expansion or reduction, does not exist 

 in the commonly assumed form of a concrete, fixed morphological entity. 

 The primitive pro-mammalian entodermal lung-tube, on the contrary, 

 must, like its lacertilian prototype, have possessed the power of selective 

 development of bronchial buds from any point of its epithelial surface. 



The characters and type of such selections have lieen determined bv 

 environmental adaptations in the widest sense. They must have from 

 the beginning represented the reaction of the milieu on pulmonary or- 

 ganization, and hence it is quite possible that we are dealing with a 

 polyphyletic ancestry of the modern mammalian lung. 



The extant ordinal types are the result of the transmission of selective 

 patterns by inheritance to the modern descendants. All our evidence 

 goes to show that the primitive lung form has, in certain groups, during 

 the progress of evolutionary descent, undergone modifications — some- 

 times of wide import — in direct response to changes in the environmental 

 adaptations of the organism as a whole. The possibility for the develop- 

 ment of these secondary adaptive modifications lies in the continued mor- 

 phogenetic plasticity of the lung tube — and in its potential capacity of 

 developing additional or atypical points of epithelial activity. 



The individual variants within a species — both secondary and cardi- 

 nal — demonstrate the possession of this capacity conclusively. Mam- 

 malian ontogeny strongly confirms this view, which affords likewise the 

 only key for the interpretation of the complicated ordinal divergence of 

 branchial types. 



Professor Schulte illustrated a number of ontogenetic variants of the 

 human kidney, such as deranged position, including inversion, of one 

 kidney and its vessels, adhesion or partial fusion of both kidneys, com- 

 plete union of the opposite kidneys into a single organ, varying degrees 

 of atrophy of one kidney. 



These abnormal conditions are made more intelligible by the ontoge- 

 netic history of the kidneys, the opposite kidneys arising in a very re- 

 stricted space and migrating thence along divergent paths to their defini- 

 tive positions. When the normal course of development is disturbed, the 

 two closely appressed glands may adhere or more or less completely unite ; 

 in the subsequent displacement, or migration of the kidneys, one or the 

 other is thus dragged out of its normal course aud assumes irregular posi- 

 tions with reference to its fellow. 



Doctor Brown illustrated certain abnormal conditions in the dorsal 

 and lumbar regions of the vertebral column, characterized by asA^mmetri- 



