SYSTEMATIC SURVEY. 101 



nous in others. A nucleus is present, and often multiplies, apparently 

 in association with reproduction. Vacuoles, contractile or otherwise, 

 seem to be very rare. Conjugation has not been certainly observed. 

 Multiplication may take place by division, but usually by the repeated 

 division of the nucleus and the formation of internal bud spores. The 

 great majority are marine, occurring at all depths. Those from great 

 depths have usually shells of glued sand ; the limy forms are found at 

 their best in the shallow water of warm seas, but some occur in the open 

 sea, and sinking down as they die form ooze. They are common as 

 fossils from Silurian strata onwards. 



Examples. Ground, in both fresh and salt water, with one or two 

 openings to its shell, which is, however, virtually enclosed in the over- 





FIG. 27. Polystomella. (After SCHULTZE.) 



flowing protoplasm ; Microgroinia socialis, in fresh water, forming 

 colonies ; Shepheardella^ with an opening at each end of a long mem- 

 branous case ; Miliolina, with a chambered cell simply coiled, and a 

 single aperture. Such forms are often called Imperforate, in contrast to 

 those whose shells have many pores. Lagena, with a simple flask- 

 shaped cell, with diffuse holes for the processes ; Globigerina, a pelagic 

 limy form, with many chambers covered with pores, contributes very 

 largely to the ooze ; Hastigerina^ a pelagic form, with bubbly protoplasm 

 abundantly overflowing round the shell .which comes to be internal like 

 a Radiolarian "central capsule" (q v.) ; Amwodiscus, from the depths, 



