. The Protozoa. Protozoa. THE SARCODINA 73 the plasm extends entirely around the shell, the new chamber almost incloses the older ones as in Nodosarina (B). In other cases the plasm may extend over one side only of the old shell, and a curvi- linear axis of growth is the result (Fig. 35, A, B, and 36, C). The spiral thus formed may be flat or coiled around a longitudinal axis as in the mollusc Trochns, giving an involute shell. This type, the most highly differentiated of all of the rhizopod shells, exhibits all grades of complexity (Fig. 37). In the highest forms each new chamber has a comple
. The Protozoa. Protozoa. THE SARCODINA 73 the plasm extends entirely around the shell, the new chamber almost incloses the older ones as in Nodosarina (B). In other cases the plasm may extend over one side only of the old shell, and a curvi- linear axis of growth is the result (Fig. 35, A, B, and 36, C). The spiral thus formed may be flat or coiled around a longitudinal axis as in the mollusc Trochns, giving an involute shell. This type, the most highly differentiated of all of the rhizopod shells, exhibits all grades of complexity (Fig. 37). In the highest forms each new chamber has a complete wall, so that the septa between the adjacent chambers consist of two lamellae, while between the lamellae there is fre-. Fig. 37. — A complex polythalamous shell (schematic) of Operculina. [CARPENTER.] The shell is represented as cut in different planes to show the distribution of the canals (a!, a", a"') ; c, c, c, the outer chambers with double walls (d, d, d), one of which is shown in sec- tion (g). The chambers communicate by apertures at the inner ends of the septa (e), and by minute pores (/"). The outside (b) of the shell is marked by the radial septa. quently a space filled with a calcareous deposit or what Carpenter ('62) calls the " intermediate ; This inter-lamellar deposit is traversed by a complicated system of canals, and the deposit itself is frequently carried out into external processes and knobs (Calcarina). In the annular or discoid types a process of budding takes place around the entire circumference instead of at a localized area, and concentric circles of chambers are thus formed (Orbitolites'). The character of the mouth-openings between adjacent chambers depends upon the nature of the outer coating. If the lime casing is perforated by numerous pores through which pseudopodia can be thrust to collect food, then each chamber is sufficient for itself, and the so-called mouth-opening is small; but if the perforations a
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