256 The Sarcodina 



The usual multilocular test opens to the outside through the aperture 

 in the last chamber. This opening, which may be single or multiple (Fig. 

 5. 38), commonly lies at the base of the chamber wall but tends to be- 

 come terminal in linear tests, shifting to the wall of the last chamber. 

 The position, size, and shape of the aperture, and the number of open- 

 ings are features of taxonomic importance. In addition to the aperture, 

 the walls of perforate tests contain many small pores. In imperforate 

 tests with a single aperture (Figs. 5. 42, 43), the ectoplasm extends to the 

 outside as a condensed oral plug (buccal ectoplasm, peduncle, raphe). 



Fig. 5. 38. Various types of apertures: A. Simple terminal, Psammonyx 

 inilcanicus, megalospheric type (after Rhumbler). B. Aperture at base of wall 

 in last chamber, Eudothyra mtdia (Pennsylvanian), x32 (after Cushman and 

 Waters). C. Terminal, with tooth, Milliamina lata, x28 (after Heron-Allen 

 and Earland). D. Aperture with broad tooth, Biloculinella olobula, x32 

 (after Cushman). E. Simple terminal, at end of coiled tube, Cornuspira 

 planorbis, x52 (after Schultze). F. Aperture with bifid tooth, Dentostoniina 

 bermudiana, xl6 (after Cushman). G, H. Multiple, radiate, NevilUna coro- 

 nata, lateral and apertural views, xl5 (after Sidebottom). I. Simple terminal, 

 in coiled test, Fischerina helix, x52 (after Heron-Allen and Earland). J, K. 

 Multiple, cribate, in wall of last chamber, Polyphragma cribosum (Creta- 

 ceous) (after Reuss). 



In perforate tests the ectoplasm emerges through the many pores as well 

 as through the aperture. 



The initial chamber is known as the proloculum. In many multilocular 

 (polythalamous) species, there are two varieties of tests differing in rela- 

 tive size of the proloculum (Fig. 5. 36, H, I). As discussed below, the 

 microspheric type (with the smaller proloculum) is produced by an or- 

 ganism developing from a zygote. The megalospheric type (with the pro- 

 portionately larger proloculum) is produced by individuals resulting from 

 schizogony. As successive chambers are added, their limits are marked 

 externally by sutures, and internally by septa (Fig. 5. 36, F, G). The 

 sutures usually appear as grooves, but may be raised or else flush with 

 the surface in some species. As each new chamber is formed, the anterior 



