HELIOZOA 



71 





2. Invested with a gelatinous layer, sometimes traversed by a firmer elastic 



network. 



Chlamydophora. Heterophils Arch. ; Mastigophrys Frenzel ; 

 Acanthocystis, Carter, 



3. Ectoplasm with distinct siliceous spicules. 



Chalarothoraca. Raphidiophrys Arch. 



4. Skeleton a continuous, fenestrated shell, sometimes stalked. 



Desmothoraca. Myriophrys Penard ; Clathrulina Cienk. ; Orbu- 

 linella Entz. 



This class were at first regarded and described as fresh-water 

 Radiolaria, but the differences were too great to escape the 

 greatest living specialist in this latter group, Ernst Haeckel, 

 who in 1866 created the Heliozoa for their reception. We 

 owe our knowledge of it mainly to the labours of Cienkowsky, 

 the late William Archer, F. E. Schulze, E. Hertwig, Lesser, 

 and latterly to Schaudinn, who has monographed it for the 

 " Tierreich " (1896); and Penard has published a more recent 

 account. 



Actinophrys sol Ehrb. (Fig. 18) is a good and common type. 

 It owes its name to its resemblance to a conventional drawing of 

 the sun, with a spherical body and 

 numerous close -set diverging rays. 

 The cytoplasm shows a more coarsely 

 vacuolated outer layer, sometimes 

 called the ectosarc, and a denser in- 

 ternal layer the endosarc. In the 

 centre of the figure is the large 

 nucleus, to which the continuations 

 of the rays may be seen to converge ; 

 the pseudopodia contain each a stiffish 

 axial filament, 1 which is covered by fig. 18. a ciinophrys sol. a, Axial 

 the fine granular plasm, showing ^f *?* cC 



Currents of the granules. The axial (From Lang's Comparative Ana- 



filament disappears when the pseudo- omy ' a 

 podia are retracted or bent, and is regenerated afterwards. This 

 bending occurs when a living prey touches and adheres to a ray, 

 all its neighbours bending in like the tentacles of a Sundew. 

 The prey is carried down to the surface of the ectoplasm, and 



1 Possibly composed of the same proteid, " acanthi n," that forms spicules of 

 greater permanence in the Acantharia among the Radiolaria (p. 75 f. Figs. 24, 25, A). 



