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takes place, the blood-corpuscles suddenly remove themselves from 
these lamellas. In consequence of this suction the thickness of the 
lamellas decreases, and the complex of the lamellas is seen to be 
Fig. 2. Pholeus phalangioides. The left ling and the surrounding region 
seen from aside; one sees through the teguments the lung, the peripulminary 
blood-lacune, the pulmonary vein (4). P, pericardial space; ¢., superior wall of the 
vestibulum of the lung; L, inferior lamella of the lung; g, genital opening d; A, posterior 
part of the cephalothorax. 
compressed (over about */,, of its thickness) at every systole; as by 
their elasticity the lamellas resume their former volume at the end 
of the systole, the white mass seems to move like an accordion one 
side-wall of which would be fastened. 
So we understand the circulation of the blood in the lungs; it is 
not a consequence of a general contraction of the pillar-cells, to 
which, with Mac Lrop, one was inclined to attribute a contractility 
of their own, but it is a passive consequence of the systole of the 
heart and the elasticity of the components. 
Inhalation and exhalation can be explained in the same way from 
these phenomena. The blood-pressure of the peripulmonary lacuna 
which always surpasses the atmospheric pressure, keeps the air- 
cavities of the lungs and the cutricular products of the lamellas 
and of the vestibulum compressed. Through the variations of this 
pressure, caused by the palpitations of the heart, the air-cavities 
become alternately smaller and larger; consequently the elasticity of 
