n PHYLUM PROTOZOA 51 



fiflagrfhihi, is. a cell provided with one or more flagcl la, 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) 



c- vac 



sh 



Fia. 3 1.— Platoum stercoreum. A, single zooid ; B, formation of colony ; e. vac. contractile 

 vacuole ; /. food particles ; nil. nucleus ; sli. shell. (From BUtschli's Protozoa, after 

 Cienkowsky.) 



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, #) 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 ove rflows , as it were, through the 

 aperture ; but, instead of formirig"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 connectio n with 

 the original shell, and communicating with i t by the original 

 MKJrture. In this way a tw o-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. 36, 8), or alternately on opposite side3 of the original 

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

 (.£), 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 



