NoiES. 449 



—what, to my knowledge, other travellers had already described— tliat 

 the AmpullariEe breathe not merely with both gills and lungs, but that 

 they do so in regular alternation; for a car tain time they inhale the air 

 at the surface of the water, forming a hollow elongated tube by incurv- 

 ing the margin of the mantle, so that the hollow surface is enclosed 

 against the water, and open only at the top. "When they have thus 

 sucked in a sufficient quantity of air, they reverse the margin of the 

 mantle, opening the tube into which the water streams. The changes are 

 tolerably frequent, once or twice in a few minutes, depending, pro- 

 bably, on the temperature. No physiological explanation of the.se 

 rhythmic alternations can, however, be at present assigned. 



Note 91, "paye 193. Fritz Miiller, the well-known naturalist in 

 Brazil, in his admirable essay. Facts and Arguments for Darmin, has 

 given us a quantity of observations on the mode and way in which 

 crabs breathe air. The modes by which this is accoinplished are very 

 various ; and even the structural relations implicated in the process, 

 which are sometimes extremely peculiar, irresistibly prove that the 

 different air-breathing Crustaceans no more constitute a natural family 

 than do the Labyrinthici among fishes. 



Note ^2, page 19.3. In a few works, distinguished for their dogmatic 

 sty?e, and intended for the use of students in medicine, it is stated that 

 these land-crabs, and above all Birgus latro, breathe no air, but only 

 water, and that the branchiae are exclusively the organs of respiration. 

 I cannot understand how so incorrect a statement can have become so 

 common, for the authors of these works cannot adduce a single experi- 

 ment which proves that in fact the introduction of oxygen into the 

 blood takes place exclusively by means of water, and through the 

 branchise. Since absolutely no physiological experiments exist on this 

 subject, this erroneous view can only rest on an interpretation — ^which 

 is acknowledged to be insufficient — of the morphological features. So 

 far as here regards Birgus latro, I have shown in the text, and in the 

 cut on page 5, that the views hitherto entertained as to the structure of 

 the branchial lungs of this animal are altogether false, and that every 

 morphological attribute is to be found in them which we should expect 

 to find in a true lung. 



Nate 93, page 195. I have before alluded to the injury that may 

 sometimes result from a superabundance of air in water, by which so 

 • large a supply may be taken in by a fish (a stickleback or an Axolotl) 

 that it may become lighter than the water and so unable to find its 

 food at the bottom. 



Note 9i, page 198. Dr. August Pauly. With regard to the lass 

 point alluded to in the text I must be allowed to make a few notes. 

 Pauly says that Lymnsese, when they are kept under water and 

 have no opportunity of inhaling air-bubbles into their lungs, keep the 

 lungs closed. A mollusc, haying its lungs filled with air, will absorb 



