The cell in development and inheritance . fuse bodily with the^gg, one having some-thing to do in forming thevacuolated cytoplasm atthe animal pole, . . theother in forming the granu-lar cytoplasm at the vege-tative pole (97, p. 42).The polar axis thus deter-mined persists as that ofthe ripe ovum. Thisseems one of the clearest cases showing the establishment of the egg-polarity through therelation of the to its environment.^ Somewhat similar nurse-cells occur in the insects, where they havebeen carefully described by Korschelt. The eggs here lie in a seriesin the ovarian egg-tubes alterna
The cell in development and inheritance . fuse bodily with the^gg, one having some-thing to do in forming thevacuolated cytoplasm atthe animal pole, . . theother in forming the granu-lar cytoplasm at the vege-tative pole (97, p. 42).The polar axis thus deter-mined persists as that ofthe ripe ovum. Thisseems one of the clearest cases showing the establishment of the egg-polarity through therelation of the to its environment.^ Somewhat similar nurse-cells occur in the insects, where they havebeen carefully described by Korschelt. The eggs here lie in a seriesin the ovarian egg-tubes alternating with nutritive cells vari-ously arranged in different cases. In the butterfly Vanessa, each^gg is surrounded by a regular follicular layer of cells, a few ofwhich at one end are differentiated into nurse-cells. These cellsare very large and have huge amoeboid nuclei, rich in chromatin(Fig. jy, A). In the ear-wig, Forfiada, the arrangement is still moreremarkable, and recalls that occurring in OpJiryotrocha. Here each 1 Cf. p. Fig. 75. — Ovarian eggs of HeVix. [Obst.] A. Earlier stage, surrounded by follicle. B. Laterstage, showing inward migration and absorption of fol-licle-cells. 152 THE GERM-CELLS %gg lies in the egg-tube just below a very large nurse-cell, which,when fully developed, has an enormous branching nucleus as shownin Fig. 163. In these two cases, again, the nurse-cell is character-ized by the extraordinary development of its nucleus — a fact whichpoints to an intimate relation between the nucleus and the metaboHcactivity of the cell.^ In all these cases it is doubtful whether the nurse-cells are sister-cells of the which have sacrificed their own development for thesake of their companions, or whether they have had a distinct originfrom a very early period. That the former alternative is possible isshown by the fact that such a sacrifice occurs in some animals afterthe eggs have been laid. Thus in the earthworm, Linnbriais terres-
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