THE HELIOZOA 23 



and to the genus Proales by Penard occurs in the ectoplasm of 

 Acanthocystis turfacca. It is probable also that the minute rods 

 that have been found in Acanthocystis turfacea (Leidy) and the 

 corpuscles in A. spinifera, Rhaphidiophrys viridis, and Heterophrys 

 myriopoda may be bacteria. 



The structure of the pseudopodia is probably very constant in all 

 the higher forms. In Elaeorhanis, Nudearia, and Hedriocystis there 

 appears to be no axial filament. In Clathrulina elegans and in 

 Elaeorlumis they are sometimes bifurcated. In a Heliozoon allied 

 to Adinophrys, Crawley (5) has recently observed that the pseudo- 

 podia are arranged in tufts at the periphery, and may either 

 remain stiff and motionless like the typical pseudopodia of Heliozoa 

 or assume lashing movements like flagella or cilia. In Adino- 

 Sj'hacrium arachnoid-eum, Penard, the pseudopodia are very long, 

 branching, and capable of anastomoses. 



The relation of the inner ends of the axial filaments of the 

 typical pseudopodia varies in a remarkable way with variation in 

 the position of the nucleus. In Actinosphaerium, where the 

 number of nuclei is very great (sometimes over 400), the axial 

 fibres end each in the neighbourhood of a nucleus, if not in actual 

 contact with its membrane, so that the relation is here similar to 

 that of Adinophrys. In a great number of genera, however, the 

 centre of the body is occupied by a deeply-staining granule first 

 discovered by Grenacher (6) and now known to behave like a 

 centrosome ; to this body the inner ends of the axial filaments are 

 attached (Fig. 6, A). There is never more than a single centrosome, 

 which may be associated with a single eccentrically-placed nucleus 

 (Acanthocystis, etc.) or with many nuclei (Gymnosphaera). 



Skeletal investments of several kinds are found among the higher 

 Heliozoa. In Elaeorhanis the body is covered by an agglutina- 

 tion of diatoms, sand-grains, etc., loosely cemented together ; in 

 Heterophrys (Fig. 2 (3)) the body is surroupded by a finely granular, 

 transparent capsule, of gelatinous consistency and quite unknown 

 composition, soluble in strong acids ; this capsule is separated from 

 the ectoplasm by a considerable space, traversed only by the radial 

 pseudopodia, which emerge through perforations in its substance. 

 The outer surface of the capsule bears delicate radial spines, shorter 

 than the pseudopodia, which are regarded by Penard as being 

 chitinous in composition on the ground that they are soluble in 

 boiling sulphuric acid. In Actinolophus the greater part of the 

 body is naked, except for a short time before encystment ; but the 

 stalk, on which the body rests, is a tube of what appears to be 

 chitin, containing one or two thread-like prolongations of the body. 

 The greater number of skeletons are, however, siliceous, the silica 

 being deposited in the form of separate or loosely-articulated plates 

 or spicules (Chalarothoraca) or as a continuous basketwork (Desmo- 



