The term "resting" is very ill-chosen, for even superficial observation shows that the relative position and characters of the internal structures of such a nucleus are constantly changing with the vital activities and functions of the cell.
For a detailed study of the nucleus in Protista, see Calkins in Arch. Protistenk. vol. ii. 1903.
The "centriole" is a minute granule sometimes recognisable in the centre of the centrosphere, and undergoing fission in advance. But centrosomes are often found without a distinction into centrosphere and centriole, and there is much confusion in the use of the terms.
The origin of the centrosomes is a problem not yet certainly solved, if indeed it be susceptible of any universal solution. They are certainly absent in many plants; and, on the other hand, structures which correspond to them often appear in mitotic divisions of Protista. In some cases the centrosomes are undoubtedly of nuclear origin, and pass out through the nuclear wall into the cytoplasm.
Though the forces at work in the dividing cell are similar in their effects to such physical forces as magnetism, static electricity, and even capillarity, and models utilising such physical forces have been devised to represent the strain-figures of the cell, the cell forces are distinct from any known physical force. For discussions of the nature of the forces at work, with bibliographies, see Angel Gallardo, Interpretatión Dinámica de la División Celular, 1902; Rhumbler, in Arch. Entw. xvi. 1903, p. 476; Hartog, C.R. cxxxviii. 1904, p. 1525, and "On the Dual Force of the Dividing-cell," pt. i. Proc. Roy. Soc. 1905 B, lxxvi. p. 548.