THE HEL1OZOA 



thoraca). In the Chalarothoraca the siliceous particles may be 

 minute and spherical, lying close together and forming one or 

 several layers (Pompholyxophrys), or they may be elongated spicules, 

 or flattened plates. Spicules are of two kinds, the one kind curved 

 and pointed at each end, the other straight, pointed or bifurcate at 

 one end, flattened and expanded at the other. The curved spicules 

 are placed tangentially to the surface of the body, and may be the 

 only skeletal elements present (Ithaphidiophrys), in which case they 

 form a loose investment for the animal, from which groups of 

 spicules are occasionally carried up the pseudopodia by the 



FIG. 4. 



Heterophrys Fockei, Archer, c.c, contractile vacuoles. A nucleus is present in the centre 

 of the protoplasm, but is not'shown in the figure, s, radial chitinous (?) spines surrounding 

 the envelope. Several xanthellae are seen in the protoplasm. (After Hertwig and Lesser.) 



streaming movement of the ectosarc (Fig. 2 (4)). In lihaphidocystis 

 some very remarkable funnel-shaped or wine-glass-shaped spicules 

 are found. In Acanthocystis both tangential scales and straight 

 spicules may be present, the latter being radially placed, with their 

 pointed ends outwards. There may be two kinds of these radial 

 spicules, a longer hollow kind with the free extremity bluntly 

 pointed, and a shorter solid kind with the free end forked (Fig. 2 (5)). 

 Siliceous plates, articulated together by their edges to form a 

 capsule round the body, occur in Pinacocystis and in Pinaciophora. 

 In Pinacocystis the pseudopodia emerge through the spaces between 

 the plates, but in Pinaciophora, according to Greeff, the plates are 

 perforated by fine pores. 



