102 PROTOZOA. 



with a flinty agglutinate shell ; Haliphysema, a form utilising sponge 

 spicules to cover itself, once mistaken for a minute sponge, or for a very 

 simple many celled animal. 



Most kinds of chalk consist mainly of the shells of Foraminifera, 

 accumulated on the floor of ancient seas ; Nummulites and related fossil 

 forms were as large as shillings or half-crowns. 



7. RADIOLARIA. Marine Rhizopods, divided by a membrane into an 

 inner central capsule (with one or more nuclei), and an outer portion, 

 giving off radiating thread-like pseudopodia. The protoplasm of the 



FIG. 28. A pelagic Foraminifer Hastigerina (Globigerina) 

 Murrayi. (After BRADY. ) 



Note central shell, projecting calcareous spines with a protoplasmic 

 axis ; also fine curved pseudopodia and vacuolated protoplasm. 



two regions is connected by openings in the capsule membrane, and 

 contains many vacuoles. No contractile vacuoles have been seen. 



There is usually a skeleton, in most cases siliceous and of complex 

 architecture, in some cases of a horn-like substance, called acanthin. 

 The skeleton may be quite outside the central capsule, or may invade it 



