ii PHYLUM PROTOZOA 51 



a flagellula, i.e. a cell provided with one or more flagella, which, 

 if its history were not known, would be included among the 

 Mastigophora. 



Platoum (Fig. 33, A) is a form resembling Microgromia, but 

 illustrating a very interesting type of colony. The protoplasm 

 flows out of the mouth of the shell in the form of a long plate (B) 



c. vac 



^^TX^\ 



-c. va,c 



FIG. 33. Platoum stercoreum. A, single zooid ; B, formation of colony ; e. vac. contractile 

 vacuole ; ./'. food particles ; nu. nucleus ; s/j. shell. (From Butsckli's Protozoa, after 

 Cieukowsky.) 



which sends off rounded side branches, and each of these, acquiring 

 a cell-wall, becomes a zooid of the simple cell-colony. 



Grromia (Fig. 34, 1} leads us to the more typical Foraminifera. 

 The protoplasm of this form protrudes from the mouth (a) of the 

 chitinoid shell (.s7f.) and flows around it so that the shell becomes 

 an internal structure. The pseudopods are very long and delicate, 

 and unite to form a complicated network, exhibiting a streaming 

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



Skeleton. Squammulina (Fig. 34,5") differs from Gromia mainly 

 in having the shell formed of calcium carbonate, so as to have 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 ; but, instead of forming an elongated plate from which 

 side buds are given off, as in Platoum, the extended 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 

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

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

 .(Fig. 35, o), 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, 5), or in a spire in which the newer chambers 



E 2 



