John Lewis Bremer 



69' 



of alveoli as a gauge. Probably in this wonderful development of the 

 (ipossum lung, the forces at work in evolution are reproduced, for the 

 lung of a new-born opossum has exactly the form of a reptilian lung." 



In the main this description is correct, but it seems to me imperfect 

 in some respects. The opossums examined by me were : first, six new- 

 born, taken from the same pouch, ranging in size from 10.5 to 13.5 mm. , 

 second, two of about 14 cm. ; third, two young adults and one old adult. 



The lungs of the smallest opossums correspond to the description of 

 Selenka, as they are composed of a few large air-chambers, opening 

 almost directly into the main bronchus, which is itself an elongated 

 chamber. The appearance in section is shown in Figs. 1 and 2, a trans- 



'card. 



Fig. 3. Fig. 4. 



Fig. 3. Cast of lung of 12.5 mm. opossum, seen from behind and from the left. 

 pr, new bronchial buds. 



Fig. 4. Cast of lung of 12.5 mm. opossum, seen from the front and a little above. 

 pr, new bronchial buds; card, cardiac lobe; It. ep, rt. ep, left and right eparterial 

 bronchi; x, x, groove for pulmonary artery. 



verse and a frontal section of a 10.5 mm. and a 12.5 him. opossum 

 respectively; and the general form is shown in Figs. 3 and 4, drawings 

 of a cast of the lung of the 12.5 mm. opossum obtained by Born's wax- 

 plate method. Selenka is wrong, however, in speaking of alveoli ; the 

 large chambers correspond to bronchi and bronchioles; infundibula and 

 alveoli are lacking. 



In the lungs of placentalia growth in the embryo is accomplished 

 by the branching of the small tubes of cuboidal cells and with narrow 

 lumen, which represent the bronchi ; each new limb in turn sends out 



