PROTOZOA 



sudden heat or certain chemical coagulants;,^ and examine it 

 under the microscope, the intermediate substance between the 

 vacuoles that we have already seen in life is again found either 

 to be finely honeycombed or else resolved into a network like 

 that of a sponge. The former structure is called a " foam " or 

 " alveolar " structure, the latter a " reticulate " structure. The 

 alveoles are about 1 /x in diameter, and spheroidal or polygonal 

 by mutual contact, elongated, however, radially to any free 

 surface, whether it be that of the cell itself or that of a larger 

 alveole or vacuole. The inner layer of protoplasm (" endo- 

 plasm," " endosarc ") contains also granules of various nature, 

 reserve matters of various kinds, oil-globules, and particles of 

 mineral matter " which are waste products, and are called 

 " excretory." In fixed specimens these granules are seen to occupy 

 the nodes of the network or of the alveoli, that is, the points 

 where two or three boundaries meet.^ Tlie outermost layer 

 (" ectoplasm " or " ectosarc ") appears in the live Amoeba struc- 

 tureless and hyaline, even under conditions the most favourable 

 for observation. The refractive index of protoplasm, when living, 

 is always well under 1-4, that of the fixed and dehydrated substance 

 is slightly over 1-6. 



Again, within the outer protoplasm is found a body of slightly 

 higher refractivity and of definite outline, termed the " nucleus " 

 (Figs. 1,2). This has a definite " wall " of plasmic nature, and a 

 substance so closely resembling the outer protoplasm in character, 

 that we call it the " nucleoplasm " (also " linin "), distinguishing 

 the outer plasm as " cytoplasm " ; the term " protoplasm " including 

 both. Within the nucleoplasm are granules of a substance that 

 stains well with the commoner dyes, especially the " basic " ones, 

 and which has hence been called " chromatin." The linin is 



1 For tlie study of the structure of protoplasm under the microscope it is 

 necessary to examine it in very thin layers, such as can for the most part be 

 obtained only by mechanical methods (section -cutting, etc.). These methods, 

 again, can only l)e applied to fixed specimens, for natural death is followed bj" 

 rapid changes, and notably by softening, -which makes the tissue less suitable for 

 our methods. We further bring out and make obvious pre-existing differentiations 

 of our specimens by various methods of staining with such dyes as logwood and 

 cochineal and their derivatives, and coal-tar pigments (see also p. 11 n. ). 



- In many Protista these granules have been shown by SchewiakotF, in Z. v-iss. 

 Zool. Ivii. 1893, p. 32, to consist of a calcium phosphate, probably CasPoOg. 



'■'■ It is not always possible to tell how much of these structures represents 

 what existed in life (see p. 11). 



