168 



CLASS: RHIZOPODA 



capsular portion (Fig. 77). The skeleton may be in the form of radiating 

 spines, tangentially arranged rods, or definite fenestrated shells (Fig. 78). 

 The latter may be spherical, with perforations, and several such shells 

 may be formed concentrically, one within the other, as the animal in- 

 creases in size, or they may have a definite axis, and be shaped like a cone 

 or bottle. In many forms the cytoplasm contains peculiar yellow cells 

 about 15 microns in diameter. These are known as zooxanthellse, and 

 each is an independent vegetable organism possessing a cellulose wall and 

 containing a nucleus and chloroplasts. It is probable that they live in 

 a condition of symbiosis with the host. The Radiolaria are marine 

 organisms which are found floating on the surface of the ocean. Their 

 shells are found in large numbers in the deposits of the ocean bed. 



4. Order: FORAMINIFERA D'Orbigny, 1826. 

 These Rhizopoda ( = Testacea Schultze, 1854) may be regarded as amoebae 

 which have the body protected by an external shell or theca. In the simplest 

 forms the shell has a single 



opening, through which the or- \ V\^ ^ tYxXv 



ganism protrudes pseudopodia ^ ^\Wv 



for locomotion purposes and 

 the capture of food, very much 



Fig. 79. — Arcella vulgaris, show- 

 ing Outline of Shell, Side 

 View of the Circulak Chro- 

 MiDiAL Body, and Two 

 Nuclei ( x 1.000). (Original.) 



Fig. 80. — Glohigerina buUoides from Ocean 

 Surface Waters ( x 70). The Shells form 

 the Main Constituent of the "Globiger- 

 iNA Ooze " of the Ocean Bed. (After 

 Ehumbler, from Lister's Article in Lan- 

 kester's Treatise on Zoology, 1903.) 



as a snail emerges from its shell (Imperforata Carpenter, 1862). Such 

 forms {Arcella, Difflugia, etc.) are very commonly found in stagnant water 

 (Fig, 79). The shells may be strengthened by adherent sand grains or other 

 material (Fig. 8). When reproduction is to take place the nucleus divides, 

 a portion of cytoplasm with one of the daughter nuclei is protruded through 

 the opening, a new shell is formed around this, and another shelled individual 



