Marvels of Pond- Life. 131 



apparatus by which the approach of two thin plates 

 of glass can be regulated by the action of a spring and 

 a screw; and just enough pressure was employed to 

 keep him from changing his place, although he was 

 able to move his tiny limbs. Thus arranged, he 

 was placed under a power of two hundred and forty 

 linear, and illuminated by an achromatic condenser,* to 

 make the fine structure of his gizzard as plain as pos- 

 sible. It was then seen that this curious organ contains 

 several prominences or teeth, and is composed of mus- 

 cular fibres, radiating in every direction. From the 

 front of the gizzard proceed two rods, which meet in a 

 point, and are supposed to represent the maxilhe or 

 jaws of insects, while between them is a tube or channel, 

 through which the food is passed. The mouth is 

 suctorial, and the two horny rods, with their central 

 piece or pieces, are protrusile. They were frequently 

 brought as far as the outer lips (if we may so call the 

 margins of the mouth), but we did not witness an actual 

 protrusion, except when the lips accompanied them, 

 and formed a small round pouting orifice. The skin of 

 the animal was tough and somewhat loose, and wrinkled 

 during the contractions its proprietor made. The in- 

 terior of the body exhibited an immense multitude of 

 globular particles of various sizes in constant motion, 

 but not moving in any vessels, or performing a distinct 

 circulation. 



* The acbromatic condenser is a frame capable of supiwrting nn 

 object glass, lower than that employed for vision, througli which the 

 light passes to the object in quantities and directions determined by 

 stops of various shapes. The appearances mentioned can be seen 

 without it, though not so well. 



