PROTOZOA 299 



body. When the animal divides, each piece receives 

 halves of all the basic parts, and therefore those also 

 that can supply the part that is wanting in each half 

 So it is with the pandorina. In the volvox two cells 

 result from the germ. One of them contains all the 

 rudimentary parts in a state of quiescence ; this is the 

 germ -cell, the rudimentary parts in which wait until 

 the animal is fully grown. But the other cell con- 

 tinues to subdivide, and as it does so the rudimentary 

 parts come into play, and produce the various volvox- 

 cells with all their peculiarities. The process is the 

 same in all the higher animals. There is always one 

 section of the cells arising from the ovum that contains 

 all the rudimentary parts in a state of slumber, as it 

 were ; these are the germ-cells. On the other hand, 

 the parts come into play in the body-cells, and give 

 distinctive characters to various groups of cells. At 

 the same time these cells lose the particular rudi- 

 mentary parts from their nuclei, and can never build 

 up an entire organism, as the germ-cells do.^ 



We have not taken into account the fact of sexual 

 generation. But we said in the seventh chapter that 



^ This is Weismann's theory. There are many exceptions, in which 

 body-cells have in their nucleus the quiescent basic parts of all the 

 sections of the body. We see this, or instance, in the phenomena 

 of regeneration. Here, if certain parts of the body are cut off, the 

 rudimentary parts that were quiescent in the cells of the contiguous 

 parts come into play, and re-build the last fragment. Plants have 

 rudimentary particles at all possible parts of the body, because any 

 sprout can reproduce a new plant. In fact, in certain plants, such as 

 the begonia, even the leaf-cells have these quiescent rudimentary 

 particles. If a begonia-leaf is set in moist soil, new plants grow 

 from it. 



