OKDER: FORAMINIFERA 



169 



separated by division of the cytoplasm. In other cases, with growth of the 

 organism, a new and larger shell, which remains adherent to the original one, 

 is formed to accommodate it. A succession of new shells may be produced, 

 and these remain attached to one another in such a way as to give rise to 

 complicated compound shells which are constant in arrangement for any 

 particular species. In addition to the main aperture the shells may have 

 numerous minute pores, through which filose pseudopodia may be pro- 

 truded (Perforata Carpenter, 1862) (Fig. 80). Reproduction of the simpler 

 forms is by binary fission, while the more complicated types may show an 

 alternation of generations with the production of flagellated gametes, as 

 described above (p. 164). The Foraminifera occur either in fresh water or 

 in the sea. The simpler ones occur in 

 the former situation, while the more 

 complicated types are marine forms. 

 Chalk deposits are composed largely 

 of shells of marine Foraminifera (Fig. 

 81). Those which occur in fresh water 

 are often placed in a separate order, 

 Thecamoebida (Delage and Herouard. 

 1896), but there is no sharp line of de- 

 marcation between these and the true 

 marine Foraminifera. Some forms, 

 such as Chlamydojphrys, may pass 

 through the intestine of an animal in 

 the encysted condition, and emerge 

 from the cyst and develop their 

 characteristic thecse in faeces after 

 they have left the body. 



Chlamydophrys stercorea Cien- 

 kowsky, 1875.— This shelled amoeba 



is of interest, as it is commonly present in fseces of such animals as horses 

 and pigs, as well as frogs and toads. In the freshly passed faeces, it occurs 

 in the encysted condition which has passed through the intestine. If 

 the faeces are kept moist for a few days or planted on agar plates, the 

 amoebae emerge from their cysts and secrete a thin, egg-shaped, trans- 

 parent shell, which has a pore at its narrower end, through which the 

 organism protrudes pseudopodia (Fig. 82). There is a single nucleus with 

 a large central karyosome. Dobell (1909) gave the measurements of an 

 average-sized individual as 20 by 14 microns. The writer, who has 

 obtained cultures from frogs' faeces as well as from dirty water, has 

 observed forms which are much smaller than this, some of them being 

 barely 15 microns in length. The organisms readily encyst. If they 



Pig. 81. — Shell of Nummulites cum- 

 mingii ( x 20). Portion of Wall 

 removed to show the chambers. 

 (From Lang, 1901, after Brady.) 



