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to say, their material consisted of erabryoiiic stages after the formation 

 of the principal bronchi was complete. The observations of these 

 investigators are only important for the specific fields in which they 

 worked, for it goes without saying, as His has suggestively remarked, 

 the conditions which govern the form development of a growing part 

 need not necessarily remain the same through the different phases 

 of its evolution. It may change its character either once or more 

 than once. 



Thus for a series of animals covering amphibia, reptilia, birds 

 (Moser, Hesser, Schmalhausen), man (His), rats and mice (Robin- 

 son), mouse, mole (Willach), rabbit (d'Hardiviller), sheep (Nicholas 

 and Dimitrova), rabbit. Echidna, cat (Narath), pig (Flint), we have 

 a general agreement, that the stem and its principle branches are 

 produced by monopodial growth. I have placed Robinson in this 

 group, partly because he believes some of the chief branches are 

 monopodial in nature but largely because, notwithstanding his own 

 use of the term "sympodial dichotomy", his own description of the 

 process of division appears to me to be essentially of a monopodial 

 character. Against these views we have the outspoken description of 

 Minot for dichotomy, in the human lung, as well as that of Blisnians- 

 KAJA. The latter does not describe the process in detail and her 

 illustrations appear to me to be capable of a monopodial interpretation, 

 especially in view of the careful work of His on the same material. 

 It is also noteworthy that she quotes the statements of Justesen in 

 supporting her ideas on the sympodial development of the chief 

 divisions of the stem. It may be recalled, however, that this author 

 did not possess in his material, stages which showed the development 

 of these particular branches. 



While it is possible to draw much harmony from the verbal de- 

 scriptions of the process of division which I have given above, there 

 are, of course, many exceptions and different complexions to these 

 views. Since, in my opinion, it makes little difference whether the 

 monopodial outgrowths take place from the end bud or from the stem 

 a little higher up, we may justifiably say that among those who have 

 studied the production of the chief bronchi of the vertebrate lung, the 

 following stand for an absolute monopodial system: Moser, Hesser, 

 Schmalhausen, His, Willach, Robinson (?), d'Hardiviller, Nicholas 

 and Dimitrova, Narath, and Flint. This series include obviously 

 all who have worked on the development of the lung during this 

 period except Minot, Blisnianskaja, and Robinson, whom I have 

 placed in both lists. Of these authors, Willach, Narath, Minot and 



