PULMONARY EVOLUTION IN MAMMALIA 105 
of his publication implies, however, that he regards it as of con- 
stant occurrence. Blisnianskaja (3), who accepts d’Hardivil- 
ler’s observations without questioning their validity, states (p. 
11) that the French author claims to have seen the evanescent 
left eparterial bud and its subsequent atrophy uniformly in all 
his embryos of the critical stages. In a careful perusal of 
d’Hardiviller’s paper I have been unable to find an explicit state- 
ment to this effect. I may have overlooked the passage referred 
to, but not quoted, by Blisnianskaja. 
To summarize this critique of d’Hardiviller’s contribution I 
would repeat that, in my opinion, his conclusions cannot be 
utilized in support of the Reduction Theory as whose main prop 
they imposed at the time of their appearance. The most plaus- 
ible interpretation, which I can give of this extraordinary pub- 
lication, is that the French investigator, by some marvelous 
chance, or owing to the perpetuation of a restricted racial char- 
acter in his material, encountered a group of variant rabbit em- 
bryos, which, if development had proceeded, would have yielded 
atypical adult individuals possessing the left eparterial bronchial 
variant described above. No warrant is hereby given for the 
assumption that such embryonic variants possess the phylo- 
genetic significance attributed to them by the author, or that 
they play the part he assigns to them in the normal ontogeny of 
the mammalian lung. 
Bremer (5) published a paper on the lung of the opossum in 
1904 in which he described his findings in younger and older 
stages of pouch-embryos of Didelphis marsupialis, L. (virginiana, 
Shaw) and in the adult of the same form. His material consisted 
of six new-born opossums, taken from the same pouch, ranging in 
size from 10.5 to 12.5 mm., two older pouch-young, of about 14 
em. in length, and three adult animals. 
In five out of six of the embryos in the youngest litter Bremer 
made Born reconstructions of the lung, the sixth proving not 
suitable for this method. He describes the presence of both a 
right and left eparterial bronchus in all of these models. Regard- 
ing the left eparterial component he says (p. 71): 
