osseuse aun r61e actif dans le processes d'ost6ite qui alilbne sa raise en libert6 par la dissolution de la substance qui l'entoure" (RmAL and VIGNAL, 1881).

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IXTRODUCTIONThe rcspiraiory system of uyuatic mammals and espccially that of whales has attracted in the past thc attention of numerous cornparativc anatomists as well as physiologists. From the point of view of the histolo,T of the respiratory portion of the lungs of aquatic mammals, a few descriptions 'nave gradually accumulated since the beginning of this century.To the latter belong the papers of Pick ('07) on Hulicore dugong ; Harbosa ( '14)' E'iebiger ( '16)' Lacoste and Baudrirnont ( '26) on the Nediterranean dolphin; Lacoste and Baudrimont ('33) on the harbor porpoise; Wislocki on the httlc-noscd porpoise ( '29) and thc Florida manatee ('35) ; Lauric ('33) arid Haynes and Laurie ( '37) on the large South Atlantic whales; Bonin and RQlanger ( '39) on thc Korth Atlantic whit c whale.All of these publications, however, have been limited mainly to a description of individual species, with the exception of Wislocki's paper on thc rnanatee ('35) which attempted to assemble certain comparative data. Finally, a recent study by Wislocki and BQlanger ( '40) has established certain salient differences between the lungs of thc larger Cctaoea and those of smaller specks.'Presented in partial fulfillmer~t of the degree of Master of Arts from the Graduate 8ehool of Arts mid Seicnees of IIarvssd University.