xxiii UNICELLULAR AND MULTICELLULAR ANIMALS 267 



the Mycetozoa and Opalina may be said to take an inter- 

 mediate place between the strictly unicellular and the multi- 

 cellular animals in much the same way as Mucorand Vaucheria 

 connect unicellular and multicellular plants. The plas- 

 modium of the Mycetozoa is formed, in the first instance 

 (p. 54), by the fusion of amcebulae : hence it is a many-celled 

 structure, the constituent cells of which have lost their 

 boundaries and are indicated only by their nuclei. Sub- 

 sequently the nuclei multiply by division, and, although 

 the process does not affect the protoplasm, it is allowable to 

 say that the number of virtual cells of which the plasmodium 

 is composed is thereby increased. The Mycetozoon, in its 

 plasmodial stage, is, in fact, a non-cellular organism, like 

 Mucor or Vaucheria. But if this way of looking at the 

 Mycetozoa is correct, it follows that Opalina is to be con- 

 sidered rather as a multinucleate but non-cellular than as a 

 unicellular animal. 



