152 



THE BEGINNINGS OF LIFE. 



definite in its morphological characters, since it is now 

 acknowledged that the cell may or may not be enclosed 

 by a membrane or cell-wall. For the structureless mass 

 of protoplasm the mere bit of plasma, or living matter 

 in which no inner differentiation has yet taken place, 

 we cannot do better than adopt HaeckePs 1 term 'plastide.' 

 The plastide, like the cell, may vary much in size : it, 

 also, may be either naked or bounded by a membrane. 



The old doctrine as to the fundamental properties of 

 the c celF as a vital unit, did well enough in those days 

 when the lowest known living things the lowest plants 

 and the lowest animals were thought to be c unicellular 



FIG. 5. 



' Unicellular Organisms.' 



a, b, c. Three of the higher Amoebae, f. One of the most minute and 



a. Nudearia simplex. simple of the unicellular Al- 



b. Amceba Limax. gse Hematococcus (Eruginosus. 



c. Amceba guttula. g. The 'red snow' Alga Prolo- 

 d and e. Gregarina Sipunculi. coccus nivalis. 



1 'Journal of Microsc. Science,' 1869, vol. ix. p. 332. 



