RHIZOPODS. 123 



6. DIFFLUGIA (Figs. 97, 98). 



Shell brown, pear-shaped, ovoid or nearly spherical, 

 and formed of angular sand -grains cemented togeth- 

 er. The upper part, the summit, may be rounded, and 

 roughened only by the edges of the sand -grains, or 

 rounded and bearing several pointed spines also form- 

 ed of sand. The lower part may be prolonged as a 

 short neck, at the end of which is the mouth for the 

 passage of the pseudopodia, or the shell may have no 

 part resembling a neck. The animal which builds 

 this protective case lives inside of it, and is a little 

 mass of colorless, or sometimes greenish, protoplasm, 

 somewhat resembling an Amoeba, and almost entire- 

 ly filling the cavity of the shell. The mouth is circu- 

 lar, and may be either smooth or with several rounded 

 teeth or lobes on its inner edge. No .part of the ani- 

 mal in any of the shell-bearing forms, except the pseu- 

 dopodia, ever passes through the mouth. When the 

 shell is made the animal never leaves it, unless it is 

 broken by the cover-glass ; then it will at times creep 

 out and die. 



The pseudopodia are blunt and colorless. They drag 

 the shell about with the mouth downward, and capture 

 food as in the naked Khizopods. When they are with- 

 drawn, the shell appears like a dead thing, and may roll 

 about the slide at the will of the observer or the mercy 

 of the currents. But often while the student is looking 

 at an apparently dead shell of sand, a blunt little color- 

 less wave issues from the mouth, lengthens and narrows, 



