EHIZOPODA. 



39 



in various ways, and often adorned with spines. The sarcode 

 of the body is usually olive brown in color, and often does 

 not quite fill the shell. 



Fig. 6. — a Acanth&metra lanceolata ; 6 Haliomma li&xaea/titTivjm^ one of the Polyeys- 

 tina (after MtiUer). 



The pseudopodia are filamentous, and exhibit a slow cir- 

 culation of granules along their borders, but they do not run 

 into one another. All the Polycystina are microscopic, and 

 they are all inhabitants of the sea. They are best known to 

 students of the microscope as the " Fossil Infusoria of Barba- 

 does," as they occur in incalculable numbers in a sandstone in 

 that island. 



In the third family {Thalassicollida, Fig. 7) are included 

 a number of singular gelatinous organisms' which may be as 

 large as an ordinary marble, but are often hardly visible to 

 the unassisted eye. They are found floating passively at the 

 surface of most seas. 



The body in all the Thalassicollida is composed of sarcode, 

 and has the power of giving off thread-like radiating pseudo- 

 podia, which sometimes run into one another and form net- 

 works. In all cases the sarcode-body appears to have the 

 power of secreting flint in some form or other. In Collo- 

 sphcera (Fig. 7, «), the flint is secreted in the form of a shell 

 or test, perforated by large apertures. In Thalassicolla (Fig. 

 7, &), the silica forms groups of needles or "spicula," scattered 

 here and there in the jelly-like sarcode. 



Oedek IV. Spongida. — The last order of the Rhizopoda 

 is that of the Spongida, the exact nature and position of 

 which have only recently been determined. For a long time 

 sponges were pretty generally regarded as being vegetables, 

 and it is only since the microscope has been employed in their 



