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ROBERT W. HEGNER 



one cleavage cell (fig. 13, D) during the first and second divisions, 

 and the cell containing it in the four-cell stage (fig. 13, E) is 

 situated dorsally. Then the nucleolus becomes vacuolated and 

 its substance slowly surrounds the nucleus, occupying a large 



Fig. 13 Copidosoma (Litomastix) truncatellus (redrawn from Silvestri, 

 '06). A, oocyte showing germinal vesicle (g.v) containing a chromatin-nucleolus 

 (c.n) and a plasmosome (p). B, egg, a few minutes after deposition, showing 

 first maturation spindle (m.s) and 'nucleolo' (A^). C, egg about one hour after 

 deposition, showing three polar bodies (p.b), the first cleavage nucleus (c.n), and 

 the 'nucleolo.' D, egg in two-cell stage, about one and one-half hours old. p.n, 

 polar nucleus. E, egg about one and one-half hours old; in four-cell stage. F, 

 egg about four and one-half hours old showing two polar nuclei dividing, two 

 embryonic cells containing nucleolar substance, and six embryonic cells (divid- 

 ing) without nucleolar substance. 



part of the cytoplasm. Division of this cell is not synchronous 

 with that of the other cleavage cells but is slightly slower. When 

 it does divide each daughter cell receives a share of the nucleolar 

 substance (fig. 13, F). Silvestri did not trace the cells contain- 



