MRS. COATES'S BATH. 71 



In the larval state this is a very peculiar creature. 

 It is long-bodied, with a blackish head, and along the 

 sides of the body are delicate white filaments, which are 

 the ' branchiae,' or gills, by which the creature breathes. 

 Eespiration is effected by a continual passage of water 

 over the gills, and in still water this object is achieved 

 by a very constant undulation of the body, so that the 

 gills necessarily are brought in contact with fresh par- 

 ticles of water. By means of the same undulations, the 

 larva urges itself through the water, just as has been 

 mentioned of the Dyticus larva, and so, by the mere act 

 of progression, increased power of respiration is obtained. 

 In perfectly still water, the creature is never quiet for a 

 moment, but keeps up a perpetual undulation of the 

 body, during which the little gills have a most graceful 

 appearance, as they float like silver threads on either side 

 of the body. Sometimes the larva obtains its supply of 

 oxygen by ascending a few inches by forcible undulations, 

 and then allowing itself to sink slowly to the bottom, 

 the delicate branchiae being spread out on either side, 

 and acting as floats to prevent it from sinking too fast. 



In 'Mrs. Coates's Bath' are numberless water- 

 boatmen (Notonecta) of various species and in all stages 

 of existence. We will, however, content ourselves with 

 the commonest and largest species. The insect derives 

 the popular name of water-boatman from the fact that 

 it lies on its back, the sharp edge of which makes a very 

 good imitation of a boat-keel, and rows itself by its long 

 swimming-legs, which are nearly straight, and, with their 



