THE CONSERVATION OF LIFE 217 



leads to a doubling of the individuality. We must also admit 

 that the unicellular organisms or at any rate the Amoebae which 

 have been the subject of this examination have this advantage 

 before us and all multicellar organisms that they possess potential 

 immortality. 



As we shall see later, many protozoa divide during reproduc- 

 tion not only into two, but three, four, and even more parts 

 which are all able to develop into complete individuals. But 

 does that justify us to speak of death ? Assuredly not, for the 

 sole difference which we are able to observe is that in these the 

 mother-individual has not only doubled, but trebled, or quadrupled, 

 or multiplied x times. The facts are so clear and incontestable 

 that one cannot see why anyone should find it difficult to accept 

 them. 



Reproduction in such a simple manner can take place only 

 in very few protozoans, because only very few have such low 

 organization. In the closely related Foraminifera it requires 

 already rather elaborate preparations before the mother may 

 proceed to fission. The Foraminifera differ from the Amoebae 

 only by the possession of a shell. We may describe them as 

 Amoebae which have made for themselves a solid shell as a 

 protection against enemies (see fig. 52). As great as are the 

 differences in shape and appearance of the shells of the individual 

 species, as different is the material which has been used in their 

 construction. Sometimes the shell is merely a delicate mem- 

 brane, a secretion of the outer protoplasm. Sometimes the 

 animalcules absorb little particles of sand, or of diatom-shells, 

 which they afterwards deposit on the surface of the body and 

 join into a firm armour by means of a chitinous glue. In others 

 the shell consists of numberless minute silica-plates, while the 

 vast numbers of marine Foraminifera make their shells by pre- 

 ference of carbonate of lime which they take from the sea 

 water and secrete, often in the form of most delicately shaped 

 shells. These marine species are of particular importance 

 to man and the history of the earth because in many parts of 

 the earth they have been the origin of enormous mountains and 

 rocks. Just as the Foraminifera are to-day found swimming in 

 the ocean in vast masses, driven by current and wind hither and 

 thither, so they must have peopled the ocean in remote ages. 



