THE PROTOZOA THE DAWN OF LIFE 9 



grains, cemented together, while in certain fresh-water forms the 

 shell is chitinoid. In all cases the shell at first has but a single 

 chamber, and in some species persists as such throughout the life 

 of the organism ; but the general tendency is for the number of 

 chambers to increase, with the result that they assume the most 

 varied forms. Indeed, as Dr. Carpenter wrote in reference to the 

 Arenaceous Forams, " There is nothing more wonderful in Nature 

 than the building up of these elaborate and symmetrical structures 

 by mere jelly-specks, presenting no traces whatever of that definite 

 organisation which we are accustomed to regard as necessary to 

 the manifestations of conscious life. The tests (shells) they con- 

 struct 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, hav- 

 ing 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, per- 

 forated with numerous small pores disposed at pretty regular 

 intervals. Another species selects the minutest sand grains and 

 the terminal portions of sponge spicules, and works them up to- 

 gether 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 the 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." 



An examination of a number of the shells or tests of different 

 species of Foraminifera will show that while in some the shell has 

 a wide opening on the exterior, in others this large opening is not 

 present, its place being taken by numerous minute pores scat- 

 tered over the surface of the shell : distinctions at one time used 

 for the purpose of classification. Thus the Foraminifera were 

 formerly classified, according to the structure of the shell, into 

 Vitreous or Perforate, Porcellanous or Imperforate, and Arena- 

 ceous ; but this classification is now considered too artificial, as 

 it separates apparently adjacent forms. Brady, who described 





