PHYLUM PROTOZOA 



55 



and unite to form a complicated network, exhibiting a streaming 

 movement of granules and serving, as usual, to capture prey. 



Skeleton. Squammulina (Fig. 36, 3) differs from Gromia mainly 

 in having the shell formed of calcium carbonate and possessing the 

 character of a hollow, stony sphere, with an aperture at one end. 

 It appears that all the calcareous Foraminifera begin life in this 

 simple form ; but in the majority of cases the adult structure 

 attains a considerable degree of complexity. The protoplasm of 

 the original globular chamber overflows, as it were, through the 

 aperture ; and the extruded mass rounds itself off, and secretes 

 a calcareous shell in organic connection with the original 

 shell, and communicating with it by the original aperture. 

 In this way a two-chambered shell is produced, and a repeti- 



FIG. 38. Hastigerina murrayi. phm. vacuolated protoplasm surrounding shell ; psd. 

 pseudopods ; sh. shell ; sp. spines. (After Brady.) 



tion of the process gives us the many-chambered shell found 

 in most genera. New chambers may be added in a straight line 

 (Fig. 37, 3), or alternately on opposite sides of the original 

 chamber (5), or with each new chamber enclosing its predecessor 

 (4), or in a flat spiral, each new chamber being larger than its 

 predecessor (7, 8), or in a spire in which the newer chambers 

 overlap the older (9, 10), or in an irregular spiral of globular 

 chambers (6), or in an extremely compact spiral in which the new 

 chambers completely enclose their predecessors (IT). In all cases 

 adjacent chambers communicate with one another either by a 

 single large hole or by numerous small ones : the protoplasm 

 is thus perfectly continuous throughout the organism. With the 



