2O 



POLYCYSTINA. 



PART III. 



Their bodies are inclosed in siliceous shells, which have 

 either the form of a thin hollow sphere perforated by 

 large openings like windows, or of a perforated sphere 

 produced here and there into tubes, spines, and a 

 variety of singular projections : so they have many 

 varied but beautiful microscopic forms. The animal 

 which inhabits these shells is a mouthless mass of sar- 

 code, divided into four lobes with a nucleus in each 

 and covered with a thick gelatinous coat. It is crim- 

 son in the Eucyrtidium and Dictyopodium trilobum of 

 Haeckel (figs. 89 and 90) : in others, as the Podocyrtis 

 Schomburgi, it is olive brown with yellow globules 

 (fig. 91). These creatures extend themselves in radiating 

 filaments through the perforations of their shells in 

 search of food, like their type the Actinophrys sol, to 

 whose pseudopodia the filaments are per- 

 fectly similar in form, isolation, and in 

 the slow movements of granules along 

 their borders. The Polycystine does not 

 always fill its shell, occasionally retreating 

 into the vault or upper part of it, as in 

 the Eucyrtidium (fig. 89, frontispiece to 

 vol. i.). Sometimes the shell is furnished 

 with radiating elongations, as in the 

 Dictyopodium trilobum (fig. 90) . In both 

 of these shells the animal consists of four 

 crimson lobes. These beautiful micro- 

 scopic organisms are found at present in 

 the Mediterranean, in the Arctic and 

 Fig. 91. Podocyrtis Antarctic seas, and on the bed of the 

 North Atlantic. They had been exceed- 

 ingly abundant during the later geological periods; 

 multitudes are discovered in the chalk and marls in 

 Sicily, Greece, at Bermuda, at Richmond in Virginia 

 and elsewhere; in all 282 different fossil forms have 

 been described, grouped in 44 genera. 



