382 EVENINGS AT THE MICROSCOPE. 



Diatom, which is thus brought into the midst of the 

 sarcode, a vacuole being new-made for its reception. 

 This, then, performs the part of a temporary stomach : the 

 digestible portions of the prey are extracted, and then the 

 insoluble shell of flint is, as it were, gradually squeezed to 

 some part of the exterior, and gradually forced out, the 

 vacuole disappearing with it, or perhaps retaining a minute 

 portion of the fluid, and thus perpetuating itself for a while. 

 This is the earliest condition in which the process of 

 digestion can be recognised. 



Another genus somewhat similar is Arcella, but it differs 

 in being furnished with a more or less rounded shell 

 (lorica), like a little box. In examining the matters that 

 adhere to the stems of duckweed, and other water plants, 

 we frequently observe little circular bodies of a yellowish 

 or reddish-brown colour, some much darker than others, 

 but all having a central round spot paler than the rest. 

 On first examination they seem inert and dead, but if we 

 closely watch one, we perceive that it is endowed with the 

 power of motion ; and we directly discern, thrust out from 

 its edge, variable processes, in the form of arms, of clear, 

 perfectly colourless, and most delicate jelly, sometimes 

 pointed, sometimes blunt, which slowly change their form 

 and position. By the aid of these, a feeble and irregular 

 motion is given to the box, which is sometimes turned 

 partly over ; when we perceive that its under side is flat 

 or probably concave, and that its outline is cut into facets. 

 The lorica is somewhat flexible, for the edges at two 

 opposite points are sometimes bent down towards each 

 other, so as to give the creature the form of a crescent. 

 The internal viscera are dimly discernible through the 

 coloured lorica, and resemble those of Amoeba. A dark 

 oval ring is commonly seen at one side, which is probably 

 the outline of the contractile bladder. It may, in fact, be 

 considered as an Ammba, whose external surface has the 

 power of secreting a symmetrical shell of horny or 



