. A manual of zoology. Zoology. 56 GENERAL PRINCirLES OF ZOOLOGY mous with the division of the cell; but to understand this wc must first consider the nucleus. This is a body enclosed in the protoplasm, whose form, though definite for each kind of cell, shows in general wide varia- tions. Usually it is spherical or oval, hut it may be elongated or rod- shaped, bent into a horseshoe, with constrictions like a rosary, or even be branched or treelike (fig. iS); in many living cells it is but little difierent. Fig. iS.â^'arious forms of nuclei, a, horscshoc-shajici! nucleus of an .\cinete; h, bran
. A manual of zoology. Zoology. 56 GENERAL PRINCirLES OF ZOOLOGY mous with the division of the cell; but to understand this wc must first consider the nucleus. This is a body enclosed in the protoplasm, whose form, though definite for each kind of cell, shows in general wide varia- tions. Usually it is spherical or oval, hut it may be elongated or rod- shaped, bent into a horseshoe, with constrictions like a rosary, or even be branched or treelike (fig. iS); in many living cells it is but little difierent. Fig. iS.â^'arious forms of nuclei, a, horscshoc-shajici! nucleus of an .\cinete; h, branching nucleus from the Malpighian vessel of a Sphmgid larva; c, rosary-shaped nucleus of Stentor ccendcus. in appearance from the protoplasm and can only be seen with care and by employment of a special technique based upon the microchemical reaction of the nuclear substance. The Nuclear Substance.âThe nuclear substance is distinguished from protoplasm, among other ways, by its greater coagulability in certain acids, , acetic and chromic, which therefore are often used for demon- strating the nucleus. In its minute structure the nucleus affords a wonder- ful variety of pictures varying according to the objects chosen. Accord- ing to their reactions to stains two substances in particular are distin- guished: chromatin or nuclein (fig. 19, cJi), which is easily stained by certain staining-fluids (carmine, ha;, satTranin), and the achromalin or linin, which stains only vmder special conditions. The achromatin forms a network or reticulum (according to another â view a honeycomb structure) filled with a nuclear fluid, bounded exter- nally by a nuclear membrane. If lillle nuclear lluid be present, and the reticulum consequently be narrow-meshed, the nucleus seems Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly rese
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
