554 



THE LOWEST ANIMALS. 



Order Foraminifera. 



If shelly sea-sand be looked over with a lens, there will often be seen tiny- 

 shells no bigger than the grains of sand amongst which they lie. The specimen 

 illustrated on p. 558, and whose shell is about one - twentieth of an inch in 



diameter, was originally named the 

 spiral nautilus, with crenated joints. 

 Another kind (Miliolina) occurs in 

 the shape of porcelain-like oval shells, 

 one -twentieth of an inch in length, 

 with about five visible segments, 

 arranged somewhat like a string of 

 sausages wound round each other not 

 quite in the same plane. Foraminifera 

 are rhizopods whose simple sarcode- 

 bodies emit slender branching pseu- 

 dopods, and which form a shell of 

 membrane, of foreign particles of 

 sand, etc., of carbonate of lime, or, in 

 rare instances, of silica. The order is 

 divided into two groups, the Imper- 

 forata and the Perforata; in the former 

 of which the shell possesses only one 

 or a few comparatively large aper- 

 tures, whereas in the latter, in addition 

 to its main opening, the shell has its 

 walls perforated all over with small 

 pores through which pseudopods can 

 be emitted. 



The Imperforata form shells of 

 membrane, agglutinated particles of 

 sand, mud, sponge-spicules, etc., or of 

 carbonate of lime ; the vast majority 

 of the Perforata form shells of the 

 last-named material. The imperforate 

 shells of carbonate of lime often resemble milk-white porcelain ; whereas the per- 

 forate shells, especially in early stages, have a glassy appearance. 



Gromia is found both in fresh and brackish water and in the sea in 

 the form of minute, oval, egg-shaped bodies about one-twentieth of an inch 

 in length, fixed on tufts of corallines, or loose in the sand and mud. At first 

 there appears to be nothing remarkable about the tiny oval mass resembling 

 the egg of a zoophyte ; but presently from the opening at one end of the 

 membranous sac or shell granular threads of sarcode creep out and become 

 fixed on the glass slide ; slender trunks of sarcode extend themselves, and divide 

 into finer and finer branches, which reunite to form a network of streaming 

 granular filaments ever changing in form, and which may extend to six or eight 



egg-shaped gromia, Gromia oviformis (magnified 

 600 diameters). 



