198 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



Lymnseidfe which breathe water throughout their lives. In the 

 course of his investigations of the deep-water fauna of the Lake 

 of Geneva, he brought up from a depth of 130 fathoms, 

 among other animals, some Lymnseae which had in their lungs 

 no air, b .t only water, and which lived there in great numbers 

 and at various ages and stages of growth. But as soon as the 

 creatures brought up by the drag-net were transferred to a small 

 vessel with water in it, both old and young soon crawled to the 

 surface, opened the orifice of their lungs, and inhaled air into 

 the respiratory cavity, which was still filled with water, and 

 with which, till within a few moments, they had breathed only 

 water all their lives. This incontrovertibly proves that an 

 organ of respiration may be able to alter its function, not only 

 gradually but quite suddenly, and the apparent contrast between 

 air and water breathing consequently loses much of the signifi- 

 cance hitherto ascribed to it. On the contrary, every water- 

 breathing organ can easily be brought to breathe in the air, if 

 only two conditions are fulfilled : First, the maintenance of 

 moisture in the respiratory surface by the condensation of the 

 water contained in the atmosphere ; and, secondly, the preven- 

 tion of the collapse of the organ, and the consequent diminu- 

 tion of the respiratory surface. 



These observations accidentally made by Forel have given 

 rise to a very interesting experimental treatment of the ques- 

 tion by Dr. Pauly. He showed that the Lymnseidaa that exist 

 in the depths of various lakes, of Geneva, Constance, and Starn- 

 berg, where they can never come to the surface to breathe, 

 can live by respiration through the skin and by using their 

 lungs as gills ; but according to Pauly the chief action is to be 

 attributed to the former. He further found that they fre- 

 quently contained air in their lung-cavities without coming to 

 the surface of the water, and that they obtained it by taking the 

 numerous air-bubbles that cling to water-plants or stones into 

 the respiratory orifice. Finally he proved by experiment that 

 a Lymnsea from deep water, which had for the first time become 

 accustomed to breathe air, never returned to water-breathing ; on 

 the contrary, it kept its respiratory cavity completely closed, and 

 breathed subsequently by the skin alone while under water. 94 



