RHIZOPODS, ACTINOPODS, SLIME MOLDS, SPOROZOA 83 



surrounded, at a center-to-center distance of about 21 m/x, by 

 six others in a consistently orderly hexagonal arrangement. 

 Filaments or septa interconnect the cylinders. As many as ten 

 separate lamellae may be present, closely layered beneath the 

 shell. Internal to these is a low-density zone of homogeneously 

 granular material, considered to be ectoplasm, and a vesicular 

 endoplasm. Cytoplasmic particulates include, in addition to 

 Golgi elements and microtubular mitochondria, two kinds of 

 solid bodies that are assumed to be fecal concentrates and 

 concretions of metabolic waste products. 



The chemical composition and the significance of the highly 

 organized lamellae are completely unknown, and their disposition 

 in the oral region was not determined. Similar packing of fibrils 

 or granular bodies in hexagonal arrays is encountered in certain 

 fibrous structures in ciliates (pp. 195, 202) and in a collagenous 

 membrane in the vertebrate eye (Jakus, 1956), but there is no 

 evidence that the packed units have anything more in common 

 than meets the eye. Hedley and Bertaud suggest as a possibility 

 that the lamellae are a unique sort of cytoplasmic surface mem- 

 brane, since no other continuous boundary was found. Certainly 

 the question merits further study. 



Sub phylum Actinopoda 



In the Subphylum Actinopoda are to be found some of the 

 most remarkable achievements in cellular architecture ever 

 attained, expressed in the incredible elegance of the secreted 

 internal skeleton. The siliceous skeletons of many of the Radio- 

 larea and Heliozoea are delicately sculptured in designs of pure 

 fantasy, while the acantharian skeleton exhibits an exquisite 

 geometric precision, based on radiating spicules occurring always 

 in multiples of ten. 



Only two attempts have been made to examine skeletal struc- 

 tures, both utilizing spicules isolated from disintegrating heliozoan 

 cells. Spicules of Heterophrys marina are not silicified; they are 

 needle-shaped and show some evidence of internal structure 

 (Wohlfarth-Bottermann and Kriiger, 1954). The siliceous spicules 

 of two species of Acanthocystis (Petersen and Hansen, 1960a) 

 included plate-like and tack-shaped units of sizes and shapes 

 characteristic of the species. 



