LESSON XIV 



FORAMINIFERA, RADIOLARIA, AND DIATOMS 



IN the four previous lessons we have learnt how a uni- 

 cellular organism may attain very considerable complexity 

 by a process of differentiation of its protoplasm. In the 

 present lesson we shall consider briefly certain forms of life 

 in which, while the protoplasm of the unicellular body un- 

 dergoes comparatively little differentiation, an extraordinary 

 variety and complexity of form is produced by the develop- 

 ment of a skeleton, either in the shape of a hardened cell- 

 wall or by the formation of hard parts in the protoplasm 

 itself. 



The name Foraminifera is given to an extensive group of 

 organisms which are very common in the sea, some living 

 near the surface, others at various depths. They vary in 

 size from a sand-grain to a shilling. They consist of variously- 

 shaped masses of protoplasm, containing nuclei, and pro- 

 duced into numerous pseudopods which are extremely long 

 and delicate, and frequently unite with one another to form 

 networks, as at x in Fig. 31. The cell-body of these or- 

 ganisms is therefore very simple, and may be compared to 

 a multinucleate Amoeba with fine radiating pseudopods. 



