24 



SYSTEMATIC ZOOLOGY 



pools or of the ocean, though some are found near the surface. 

 The pseudopodia may be either blunt processes, not greatly 

 attenuated, or long and filamentous and often anastomosing 

 with one another by means of lateral processes. In many of 

 the Foraminifera pseudopodia may be formed at any point on 

 the surface of the body, but when several appear near one point 

 there results a movement of the whole animal in that direction. 

 Thus when the animal is moving we may speak of an anterior 



end, that which is in ad- 

 vance, and a posterior 

 end, and it has been 

 observed that the nu- 

 cleus and the contractile 

 vacuole lie near the pos- 

 terior end. When the 

 animal is at rest, how- 

 ever, it becomes im- 

 possible to make this 

 distinction. 



The order derives its 

 name from the fact 

 that the skeletons or 

 shells are in many cases 

 pierced by numerous 

 minute holes through 

 which the pseudopodia 

 may be protruded. A 

 skeleton is not always 

 present, however, and 

 some of the skeletons 

 have only one large opening for the protrusion of the pseudo- 

 podia, and no minute pores. The shell may consist of a secreted 

 membrane of chitin, or it may be merely a gelatinous secre- 

 tion in which small particles of sand, diatoms, etc., have become 

 embedded, or it may be composed of a secretion of calcium car- 

 bonate, and this is true of most of the marine Foraminifera. In 

 a very few cases the shell is siliceous. 



Of those that are naked, i.e. without skeletons, the fresh-water 

 genus, Amoeba (Fig. 2), contains characteristic examples. They 



]•'!<;. 4. ./, Quadrula symmetrica; if, Hyalosphenia 

 lata; (', Arcella vulgaris; l>, />//f//t^ r /<i pyriformis. 

 (After Schulze and Wallich, from Parker and Has- 

 well's Mann il. j 



