I PHYLUM PROTOZOA 23 



but usually a size larger, remaining in firm connection with 

 it, the cavities of the two remaining in communication with 

 one another through the original opening or openings at 

 which the bud first appeared. From this second shell in 

 turn a bud is given off in the same manner, and the process 

 is repeated again and again, until, instead of a single particle 

 of protoplasm enclosed in a single shell, there is formed a 

 composite structure, made up of a number of particles of 

 protoplasm, each with its nucleus, and each enclosed in a 

 shell, the whole of the shells being firmly united togethei, 

 and the whole of the particles of protoplasm being in con- 

 tinuity through the apertures of communication. The 

 several parts of such a compound shell, which are known as 

 the chambers, are variously arranged in different Forami- 

 nifera (Fig. 5), according to the way in which the succes- 

 sive buds have been given off. In some the buds succeed 

 one another in a straight line, and the compound shell 

 which results (j) has consequently its chambers arranged 

 in a straight row. Or the chambers may be developed 

 alternately on opposite sides of the original cell (5), or 

 with the new chambers entirely overlapping their prede- 

 cessors (4). In other cases the development of the buds 

 takes a winding course, the resulting shell having its cham- 

 bers arranged in some form of spiral, like the spiral of a 

 watch-spring or of a corkscrew. Such a spiral shell (6 — 11) 

 assumes a great variety of forms in different Foraminifera, 

 owing to differences, not only in the shape of the chambers 

 themselves, but also in the nature of the spiral in which they 

 are arranged. 



In many cases the shell is further complicated by the 

 development of what is termed the supplemental shell (Fig. 

 5, 8 &), a deposit of carbonate of lime outside the original 

 shell, traversed by a complex system of fine canals contain- 



