62 VIGNETTES FROM INVISIBLE LIFE. 



presence therefore is ascertained only by chemical 

 re -agents. The Amoeba, consequently, is not all 

 pure protoplasm, and must take its rank among 

 organic structures : it approaches the dignified 

 position of a true cell, and is fairly on its way to 

 higher grades in the animal creation. In fact, 

 it has already reached a higher grade ; for here 

 are true Amoeba (Arcella and Dijflfagia) enclosed 

 in something more than an in visible membrane. 

 These have something so dense to protect them 

 that it may be called a shell. 



Arcella and Diffluyia are testaceous Amoeba ; 

 the former having a horny covering, and the latter 

 an envelope made of particles of sand, shell, and so 

 forth, cemented into a sort of pitcher open at one 

 end, whence the " filmy fingers " of its inhabitant 

 protrude in search of food. The home of the Arcella 

 is egg-shaped, and delicately marked with a minute 

 and regular pattern. We thus approach one of the 

 most wonderful operations of nature, and one which 

 is still involved in much obscurity namely, the 

 formation, of shells, or rather the marvellous form, 

 markings, patterns, and appropriate colours which 

 are produced under this name. Curiously enough, 



