8UBKINODOM PROTOZOA. 



17 



through which the pseudopodia are emitted. The successive 

 chambers are arranged in various ways, sometimes end to end 

 as in Nodosaria, sometimes alternately on opposite sides of an 

 axis as in Textularia, sometimes as a spiral as in Globigerina, 

 sometimes as a helix as in Rotalia (Fig. 5), and sometimes 

 more or less irregularly as in Acervularia. 





' /, '/'I ' ' 



'- 

 . 



FIG. 5. Rotalia venata (after M. SCHULTZE from HATSCHEK). 



Notwithstanding the complexity of the shell, however, the 

 protoplasm retains throughout the order its simple structure, 

 and though in the more complicated forms the single nucleus 

 may be replaced by several, yet beyond this they present no 

 more marked differentiation than is found in the simpler 

 genera. 



2. Order Heliozoa. 



In the second order, the Heliozoa, the pseudopodia are 

 slender as in the calcareous Foraminifera and are permanent 

 and somewhat rigid, the central protoplasm of each one 

 being differentiated into an elastic axial support. The ani- 

 mals are usually globular in shape, the slender pseudopodia 

 radiating out from the central mass, an appearance being 

 thus produced which is sufficient cause for the popular term 

 "sun-animalcule ".which is applied to several of the genera, 

 such as Actinophrys and Actinosplirerium (Fig. 6). Currents 



