64 PROTOZOA 



whatever of that definite organisation which we are accustomed 

 to regard as necessary to the manifestations of conscious life. . . . 

 The tests (shells) they construct when highly magnified bear 

 comparison with the most skilful masonry of man. From 

 the same sandy bottom one species picks up the coarsest quartz 

 grains, unites them together with a ferruginous cement, and thus 

 constructs a flask-shaped test, having a short neck and a single 

 large orifice ; another picks up the finer grains and puts them 

 together with the same cement into perfectly spherical tests of 

 the most extraordinary finish, perforated with numerous small 

 pores disposed at pretty regular intervals. Another species 

 selects tlie minutest sand grains and the terminal portions of 

 sponge-spicules, and works them up together — apparently with 

 no cement at all, but by the mere laying of the spicules — into 

 perfect white spheres like homoeopathic globules, each showing 

 a single-fissured orifice. And another, which makes a straight, 

 many-chambered test, the conical mouth of each chamber 

 projecting into tlie cavity of the next, while forming the walls 

 of its chambers of ordinary sand grains rather loosely held 

 together, shapes the conical mouths of the chambers by firmly 

 cementing together the quartz grains which border it." The 

 structure of the shell is indeed variable. The pylome may be 

 single or represented by a row of holes (Peneroplis, OrbitoHtes), 

 or, again, there may be several pylomes (Calcituba) ; and, again, 

 there are in addition numerous scattered pores for the protrusion 

 of pseudopodia elsewhere than from the stylopodium, in the 

 whole of the " Vitrea " and in many " Arenacea " ; and, as we 

 shall see, this may exercise a marked influence on the structure 

 of the shell. 



In some cases the shell is simple, and in Cornuspira and 

 Spirillina increases so as to have the form of a flat coiled tube. 

 In Calcituba the shell branches irregularly in a dichotomous 

 way, and the older parts break away as the seaweed on which 

 they grow is eaten away, and fall to the bottom, while the 

 younger branches go on growing and branching. The fallen 

 pieces, if they light on living weed, attach themselves thereto' 

 and repeat the original growth ; if not, the protoplasm crawls 

 out and finds a fresh weed and forms a new tube. In the 

 " Polythalamia " new chambers are formed by the excess of the 

 protoplasm emerging and surrounding itself with a shell,. 



