CHAPTER XV 



ORDER 2 MYCETOZOA DE BARY 



THE MYCETOZOA Were formerly considered to be closely re- 

 lated to fungi, being known as Myxomycetes or Myxogas- 

 teres (the "slime molds")- Through extended studies, of their 

 life-histories, de Bary showed that they are more closely related 

 to the Protozoa than to the Protophyta, although they stand 

 undoubtedly on the border line between these two groups of 

 organisms. The Mycetozoa occur on dead wood or decaying 

 vegetable matter of various kinds. 



The most conspicuous part of a mycetozoan is its Plasmo- 

 dium which is formed by the cytoplasmic fusion of several 

 myxamoebae (amoebulae) without nuclear fusion, thus pro- 

 ducing a large multinucleate protoplasmic body (Fig. 69, a). 

 The greater part of the cytoplasm is granulated, although there 

 is a thin layer of hyaline and homogeneous cytoplasm surround- 

 ing the whole body. The numerous vesicular nuclei are dis- 

 tributed throughout the granular cytoplasm. Many small 

 contractile vacuoles are present in the peripheral portion of the 

 Plasmodium. The nuclei increase in number by multiplication 

 as the body grows. The nuclear division seems to be amitotic 

 during the growth period of the Plasmodium, but is mitotic prior 

 to the spore-formation. The granulation of the cytoplasm is due 

 to the presence of enormous numbers of granules, which in Cal- 

 carinea are made up of carbonate of lime. The Plasmodium is 

 usually colorless, but sometimes yellow, green, or reddish. This 

 coloration is due to numerous droplets of a fluid pigment scat- 

 tered throughout the body. 



The food varies in different species. The great majority feed 

 on decaying vegetable matter, but some, such as Badhamia, 

 devour living fungi. Thus the Mycetozoa are holozoic or sapro- 

 zoic in their method of nutrition. The Plasmodium is alkaline 

 in reaction as a whole. Pepsin has been found in the plasmodium 

 of Fuligo and is perhaps secreted into the food vacuoles, into 



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