FORAMINIFERA AND RADIOLARIA. 



ber of specimens to tlie glass slide at once, and by grinding them down 

 together ( 192, note). For the preparation of sections, however, of the 

 extreme thinness that is often required, those which have been thus 

 reduced should be transferred to separate slides, and finished-off each one 

 by itself. 



KADIOLAHIA. 



499. It has been shown that one series of forms belonging to the 

 Rhizopod type is characterized by the radiating arrangement of their rod- 

 like pseudopodia ( 399), suggesting the designation Heliozoa or ' sun-ani- 

 malcules;' and that even among those fresh- water forms that do not depart 

 widely from the common Actinophrys (Fig. 285), there are some whose- 

 bodies are inclosed in a complete siliceous skeleton. Now just as the 



Flo. 345. 



Fossil Radiolaria from Barbadoes. a, Podocyrtis mitra; 6, Rhabdolithus sceptrum; c, Lych- 

 nocanium falciferum; d, Eucyrtidium tubulus; e, Flustrellaconcentrica;/, Lychnocaniumlucerna; 

 </, Eucyrtidium elegans; 7i, Dictyospyris clathrus; i, Eucyrtidium Mongolfieri; k, Stephanolithis 

 spinescens; I, S. nodosa; m, Lithocyclia ocellus; n, Cephalolithis sylvina; o, Podocyrtis cothur- 

 nata; p, Rhabdolitlius pipa. 



Eeticularian type of Khizopod life culminates in the marine calcareous- 

 shelled Foraminifera, so does the Heliozoic type seem to culminate in 

 the marine Radiolaria; which, living for the most part near the surface 

 of the ocean, form siliceous skeletons (often of marvellous symmetry and 

 beauty), that fall to the bottom on the death of the animals that pro- 

 duced them, and may remain unchanged, like those of the Diatoms, 

 through unlimited periods of time. Some of these skeletons, mingled 

 with those of Diatoms, had been detected by Prof. Ehrenberg in the 

 midst of various deposits of Foraminiferal origin, such as the Calcareous 

 Tertiaries of Sicily and Greece, and of Oran in Africa; and he established 

 for them the group of Polycystina, to which he was able also to refer a 

 beautiful series of forms making-up nearly the whole of a siliceous 



