MICROSCOPIC EMPIRE BUILDERS 13 



additional shelter and food. Such are the Sarcodina, 

 the group of which the well-known Amoeba of pond- 

 water the Proteus animalcule (Fig. i) of the early 

 microscopists and the Amoebae causing human 

 amoebic dysentery, are familiar members. Some of 

 the free-living members of the Sarcodina secrete or 

 form skeletons, and are founders of parts of our 

 country in a very real sense. The chalk hills of the 

 South of England consist of the skeletons of millions 

 of minute Sarcodina known as Foraminifera, while 

 the ooze at some river mouths which forms 

 plains in certain European districts consists of the 

 silicious remains of countless myriads of other 

 Sarcodina known as Radiolaria. Further, these 

 microscopic empire builders are still continuing their 

 work and adding to the land content of the world in 

 many parts. 



Some of the most beautiful Protozoa are the group 

 of Sarcodina called the Heliozoa, or sun-animalcules, 

 from whose graceful bodies pass out myriads of 

 tenuous, radiating threads, used for defence, loco- 

 motion, and obtaining food. Though their external 

 appearance recalls that of the Foraminifera, yet, 

 unlike the latter, they have no hard skeleton, and 

 their fragile bodies never form deposits in the way 

 that those of the Foraminifera and Radiolaria do. 



The Mycetozoa are a group of Protozoa claimed 

 equally by botanists and zoologists. To the botanist 

 they are the Myxomycetes or slime fungi ; to the 

 zoologist they are animals, the Mycetozoa, a branch 

 of the Sarcodina. It is no part of the work of the 

 present authors to attempt to decide the relative 



