S8 Protozoa. 



multilocularj i.e., divided by transverse septa into several small 

 cavities, whicli, however, communicate by small pores in the septa, 

 so that the protoplasm is continuous. Such shells are either 

 straight or spirally coiled, a character which may also obtain in 

 the unilocular shells; and they often closely resemble a nautilus 

 shell in miniature. Both unilocular and multilocular shells may 

 either be perforate, i.e., having besides the larger opening, 

 numerous fine pores, through which the protoplasm may extend; 

 or they may be imperforate, without such apertures. In 

 the Perforata and in some Imperforata the shell hes actually 

 within the protoplasm, for its surface is covered by the 

 overflow of protoplasm. The shells either consist of a chitiuous 

 material, to which grains of sand or other foreign bodies are often 

 firmly cemented ; or they are composed entirely of calcium 

 carbonate as in most marine forms (the calcareous shell may 

 also be strengthened by the incorporation of foreign bodies). 



The protoplasm is usually homogeneous throughout, but some- 

 times there is a superficial layer which differs from the rest in its 

 hyaline appearance and in the absence of granules, although not 

 sharply separated off from the inner granular portion. Pigment 

 granules frequently occur in the protoplasm ; there are often vacuoles, 

 which are as a rule non-contractile. The nucleus is of simple 

 spherical form; occasionally there are several, sometimes many, 

 present. The pseudopodia are either broad lobes (Pig. 1, 

 Pig 47 A), or delicate threads which then radiate out in great 

 numbers, and frequently anastomose (Pig. 47 C) ; these thin pseudopodia 

 are often of considerable length, and may be even as much as ten 

 times as long as the shell. The animal moves by means of its 

 pseudopodia, crawling about at the bottom of the sea, over plants, 

 etc. ; by means of them also, it surrounds microscopic organisms or 

 decayed organic fragments, and thus feeds upon them. 



Comparatively little is known as to their reproduction. 

 Simple binary fission has been observed in various Rhizopods ; 

 in the forms with shells, one of the newly-developed individuals 

 usually constructs a new shell, whilst the other remains in the old 

 one ; or both may leave the original shell, and form new ones. 

 Sometimes, also, a large number of smaller individuals may arise 

 within an older organism. 



Some of the Rhizopods inhabit freshwater; some are found in 

 moss or damp earth, a few upon dung, a few are parasitic {e.g. Amoeha 

 coli, in the human intestine) . The majority, however, are marine, 

 they are usually found crawling about on marine plants, colonial 

 animal^, or on the ground, usually at no great depth. A few forms 

 are Pelagic, swimming about in the open sea, often in great numbers ; 

 as they die their shells sink to the bottom, where they are 

 met with in the extensive deposits composed of their remains 



