45 6 



THE POPULAR SCIENCE MONTHLY. 



body ; and their form lias given to this class the scientific name Lamel- 

 libranchiata plate-gills. The water bathing the gills is constantly 

 renewed by means of cilia. " Wonderful, indeed, is the elaborate 

 mechanism employed to effect the double purpose of renewing the re- 



Ex. siphon. 



3 In. siphon. 



Fig. 11. Lamellibranch, siioy.-ino two Siphons. (After Horse.) 



spired fluid and feeding the helpless inhabitants of these shells. Every 

 filament of the gill-fringe, examined under a powerful microscope, is 

 found to be covered with countless cilia, in constant vibration, caus- 

 ing, by their united efforts, powerful and rapid currents. ... So ener- 



h 



l 



Fig. 12. Tracheal System indicated wiTniN tiie Outline a op a Water-Eug, b of the 

 Larva op an ^Eschna. The trachea? are 6haded. 



getic, indeed, is this ciliary movement over the entire extent of the 

 branchial organs that, if any portion of the gills be cut off with a pair 

 of scissors, it immediately swims away, and continues to row itself in 



