OF THE CELL THEORY 163 



Protozoa. In the young of many forms no nucleus 

 can be detected, while the adult possesses a con- 

 spicuous one. Some forms, as Amoeba, have a 

 single nucleus ; others, as Opalina, or Arcella, have 

 many nuclei. In Paramcecium there are two 

 nuclear structures, the nucleus proper and the 

 paranucleus, which have different properties and 

 very different functions. Then as to shape, the 

 nucleus is in most cases spherical or approximately 

 so ; in Vorticella it is greatly elongated ; in Sten- 

 tor it is elongated, and furthermore constricted in a 

 moniliform manner ; and in such forms as Dendro- 

 soma it presents an extraordinarily branched and 

 extremely complex condition. A still more curious 

 state is seen in Opalinopsis, an Infusorian living 

 parasitically in the liver of the squid. Here the 

 nucleus appears at times as a much branched reti- 

 cular structure extending the whole length of the 

 animal ; at other times the reticular nucleus breaks 

 up or becomes " pulverised " into an immense 

 number of extremely minute particles, which be- 

 come diffused through the protoplasm of the animal, 

 and would most certainly escape detection but for a 

 knowledge of their previous condition. These few 

 illustrations will serve to show how extraordinarily 

 variable the nucleus may be even amongst the 

 Protozoa. I shall return later on to the condition 

 of the nucleus in higher animals, but propose first 

 to deal with the cell-body itself. 



The cell- body or cell contents i.e., the whole 

 cell except the cell membrane and the nucleus were 

 spoken of by Dujardin as consisting of " sarcode," 



