" PHYLUM PROTOZOA 51 



^ flagclhda , 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. 34, 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) 



Fig. 34. — Platoum stercoreum. A, single zooid ; B, formation of colony ; c. vae. contractile 

 vacuole ; f. food particles ; nii. nucleus ; sh. shell. (From BUtschli's Protozoa, after 

 Cienko'wsky.) 



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

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



Gromia (Fig. 35, 1) leads us to the more typical Foraminifera. 

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

 chitinoid shell {sh.) 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. 35, 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 ; 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 chamber.s may be added in a straight line 

 (Fig. 36, 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 



E 2 



