. The American journal of anatomy . atic cross section of ahypothetical reconstruction of this bronchial type would appearas in figure 4^. Migration then becomes responsible for the re-distribution of the components shown in figure 4®. The pulmonary organization represented in figure 4^ is notfound in the phyletic series. If this is accepted as indicating the earliest phylogenetic mam-malian type of bronchial organization, one of two conclusionswould be inevitable: a. Either the mammalian lung represents the persistence of amore primitive pulmonary type than that found in the embryoor adult of
. The American journal of anatomy . atic cross section of ahypothetical reconstruction of this bronchial type would appearas in figure 4^. Migration then becomes responsible for the re-distribution of the components shown in figure 4®. The pulmonary organization represented in figure 4^ is notfound in the phyletic series. If this is accepted as indicating the earliest phylogenetic mam-malian type of bronchial organization, one of two conclusionswould be inevitable: a. Either the mammalian lung represents the persistence of amore primitive pulmonary type than that found in the embryoor adult of any of the extant lower vertebrates, or PULMONARY EVOLUTION IN MAMMALIA 139 b. The mammalian lung is a cenogenetic structure and doesnot represent the end-link in a continuous evolutionary is no phyletic relation between it and the lungs of the lowervertebrates. Neither of these hypotheses is tenable. On general phylo-genetic grounds the migratory theory not only receives no sup-port, but is positively Vm^ Fig. 4^ Their subsequent redistribution through migration. V., ventral;V-L., ventro-lateral; D., dorsal; Dm., dorso-medial; M., medial; V^n., ventro-medial. Hesser, in his important and thoroughly scientific paper onthe development of the reptilian lung (22) voices this funda-mental objection to the migratory theory admirably. In dis-cussing the much-mooted question of monopody versus dichotomyin the development of the bronchial system he says (p. 301): Stellt man das, was Narath an verschiedenen Stellen geaussert hatiiber den phylo- und ontogenetischen Ursprung der vom Stammbron-chus ausgehenden Aste, zusammen, so kommt man zu einem Resultat,welches schon an und flir sich unwahrscheinlich erscheinen muss, undwelches im Lichte des Baues der niederen Lungenformen als falschbezeichnet werden muss. Er sagt namlich, dass nicht nur die dor-salen Seitenbronchien in ihrer ersten Entstehung mit den ventralenzusammengelenkt sind, sondern dass auch die so
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