RHIZOPODS, ACTINOPODS, SLIME MOLDS, SPOROZOA 85 



cross-section, somewhat thicker than the filaments of Actino- 

 sphaerium, and rather resemble the finer tubular elements of the 

 cytoplasmic membranous reticulum. The authors of these two 

 studies used different fixatives, at different pH's, and it is impos- 

 sible to say at this point whether the difference between filaments 

 and tubules is a real one or represents the effects of the fixing 

 agents. Preservation of other components appears to be somewhat 

 better in the micrographs of Anderson and Beams. 



Neither of the pairs of authors offers any comment on the 

 surface membranes of their cells. In Wohlfarth-Bottermann and 

 Kriiger's picture of an axopodium, the surface structure is dis- 

 continuous; this could be a fixation artifact. In the micrograph 

 by Anderson and Beams, there appears to be continuous membrane 

 following the contours of the surface vacuoles and covering the 

 cytoplasm between. At the magnification provided, this seems to 

 resemble the unit membrane of any other cell. This is of interest 

 in view of Jahn and Rinaldi's speculations concerning the 

 protoplasmic surface of the Allogromia pseudopodial reticulum. 

 Since particles adhering to the surface move with the underlying 

 cytoplasm, a continuous membrane over the two antagonistic 

 streaming units is hard to imagine, yet no suggestion of a line of 

 demarcation between them is detectable with the light microscope. 

 None of the published illustrations of the heliozoa includes a 

 complete transection of an axopodium, which may be taken to 

 mean that these competent and experienced workers observed 

 nothing startling in such micrographs. 



In the cell body of the heliozoa, the axial filaments of the 

 axopodia continue deep into the endoplasm. In Actinophrys, they 

 insert directly on the membrane of the single nucleus. In Actino- 

 sphaerium they are found close to the nuclei but apparently not 

 directly connected to them. No centrioles or kinetosome-like 

 structures were seen. The nuclei have double membranes, a finely 

 granular nucleoplasm, and numerous dense, peripheral, small 

 nucleoli. The endoplasmic matrix is fairly compact, containing 

 abundant endoplasmic reticulum some of which bears Palade 

 particles. Similar granules occur free of membranes. Also 

 included in the endoplasm are microtubular mitochondria, Golgi 

 bodies, food vacuoles surrounded by a multitude of small vesicles 



