302 ANATOMY OF THE LAMELLIBRANCHIATA. 



evaporation of the water within their valves is prevented. — 

 The Uniones and Anodontae will live a very long time in mud 

 without the access of any other water than that contained in 

 it. * It has been said that salt water bivalves will live in fresh 

 water, and vice versa. Freminviller 2 states, that the Unio, 

 Anodonta, and Cyclas, are found in the Gulf of Livonia, to- 

 gether with the Tellina, Venus, &c. Nilson 3 says the same 

 of some part of the Norwegian shore. From the following 

 experiments the reader will perhaps conclude that in these 

 places there is an influx of both salt and fresh water. To as- 

 certain whether respiration could go on, the habitat being so 

 changed, the author took a portion of the branchiae of a Mac- 

 tra, and placed it in fresh water for one minute ; the cilia, 

 strongly in action befere the experiment, stopped in their vi- 

 bration, and could not be restored by immersion in sea water. 

 Five grains of common salt were added to an ounce of fresh 

 water, and a portion of the branchiae placed in the solution, 

 when the vibration ceased. In a solution of ten grains of 

 common salt to an ounce of fresh water, the vibration was 

 continued, as it was in a solution of twenty grains to the ounce. 

 In a solution of thirty grains to the ounce, it went on for a 

 time, but shortly stopped. After a portion of branchial mem- 

 brane had been stopped in its action by momentary immersion 

 in a strong brine, or in fresh water, it was restored by the se- 

 cond solution of ten grains to the ounce ; but a Mactra, of 

 which the branchiae were exposed for a longer period to the 

 action of fresh water, did not recover itself, though directly 

 afterwards returned to its native element. Sea water, or a 

 solution of two grains of common salt to an ounce of fresh 

 water, immediately stopped vibration in the Cyclas, and other 

 fresh-water-breathing Mollusca. A minute quantity of car- 

 bonate of soda added to fresh water, and a rather greater 

 quantity dissolved in sea water, rendered them irrespirable. 

 It would seem from this, that although perhaps some of these 

 animals may bear a slight change as to the freshness or salt- 

 ness of the water, (and perhaps those species inhabiting estu- 

 aries do so more than others), yet this capacity must be very 

 limited. The Cardia, Madras, Amphidesmae, &c, found in 

 marshes on the coasts, become diseased and die when the 

 water becomes concentrated by evaporation, or when it loses 

 its saltness by mixture with fresh. The Mytili found in fresh 

 water docks, are probably fresh- water species brought from 



1 Beudant, sur la possibility de faire vivre des Mollusques fluv. dans les 

 eaux salees. Stark, Brewst. Edinb. Jour., iv. Adanson, Acad. Sci. 1789. 

 2 Jamieson's Edin. Journ. vol. iv. 3 Mollusca of Sweden. 



