SARCODINA 71 



of generations in the life cycle, the microspheric form reproducing 

 asexually while the megalospheric form produces gametes. 



Most foraminifera are creeping organisms, but the Globigerinidae 

 are planktonic and have, correspondingly, vacuolated ectoplasm and 

 long slender spines on the shell. The shells of such forms, falling to 

 the bottom, form an important constituent of many deep-sea oozes. 



Allogromia (Fig. 64). Shell one-chambered, egg-shaped, pseudo- 

 chitinous. Marine and in fresh v^^aters. 



Rhabdammina (Fig. 6 A). Shell one-chambered, straight or forked, 

 tubular, composed of foreign particles. Marine. 



Nodosaria (Fig. 6 B). Shell perforate, calcareous, consisting of 

 several chambers arranged in a longitudinal row, the mouth of each 

 chamber opening into the next younger and larger. Marine. 



Polystomella (Figs. 65, 66). Shell perforate, calcareous, consisting 

 of numerous chambers, arranged in a flat spiral, and complicated as 

 follows in the details of their architecture: each whorl is equitant, 

 i.e. overlaps the previous whorl at the sides and thus hides it; the 

 mouth is replaced by a row of large pores ; backward pockets {retral 

 processes) stand along the hinder edge of each chamber; the sup- 

 plemental layer contains a system of canals filled with protoplasm. 

 Marine. The life cycle of this genus, which shows the alternation of 

 generations described above, has been followed in detail (Fig. 66). 



Nummulites (Fig. 63). As Polystomella but with more chambers. 



Globigerina (Fig. 6 C). Shell perforate, calcareous, chambers 

 fewer and less compact than in Polystomella, arranged in a rising 

 (helicoid) spiral, and bearing long spines. External layer of proto- 

 plasm frothy, with large vacuoles by which the specific gravity is 

 reduced. Marine, pelagic. 



Order RADIOLARIA 

 Marine, planktonic Sarcodina, which have no shell but possess a 

 central capsule and usually a skeleton of spicules ; whose pseudopodia 

 are fine and radial and usually without conspicuous axial filament; 

 and the outer layer of whose protoplasm is highly vacuolated. 



The pseudopodia branch, and to some extent join: they are said to 

 contain an axial filament and they show streaming of granules. The 

 central capsule is a pseudochitinous structure, of varying shape accord- 

 ing to the species, which encloses the nucleus and some cytoplasm 

 containing oil globules. It is perforated by pores, which by their 

 arrangement characterize the suborders, being evenly distributed in 

 the Peripylaea (Spumellaria), gathered into groups in the Actipylaea 

 {Acantharia), concentrated into one '*pore plate" in the Monopylaea 

 (Nassellaria), and represented by three openings or "oscula" in the 

 Tripylaea {Phaeodarta). The spicules are usually siliceous, but in one 



