Die Zelle in der Entwicklung und Vererbung. n, zu glauben, dass die Follikel - Zellen sind immediatelyconcerned mit der Übertragung von Nährstoff in die Eizelle. Eine Anzahl von Beobachtern erhalten haben, dass die Follikel - Zellen können actuallymigrate in das Innere des o. gg, und dies scheint im Fall der Manteltiere und Muscheln (Abb. definitelyestablished zu sein. 75).^ solche Fälle sind jedoch äußerst selten; und in der Regel den materialelaborated durch die nutritive Zellen in die o^gg entweder in- Lösung übergeben wird oder in Form von Granulat oder protoplasmic Substanz.^ Aninteresting Fall dieser Art auftritt

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The cell in development and inheritance . n to believe that the follicle-cells are immediatelyconcerned with the conveyance of nutriment to the ovum. A num-ber of observers have maintained that the follicle-cells may actuallymigrate into the interior of the o.gg, and this seems to be definitelyestablished in the case of the tunicates and mollusks (Fig. 75).^Such cases are, however, extremely rare; and, as a rule, the materialelaborated by the nutritive cells is passed into the o^gg either in solu-tion or in the form of granular or protoplasmic substance.^ Aninteresting case of this kind occurs in the cycads, where, accordingto Ikeno (98), the egg-cell is connected with the surrounding cellsby broad protoplasmic bridges through which cytoplasmic materialflows directly into the egg-cell. Very curious and suggestive conditions occur among the annelidsand insects. In the annelids the nutritive cells often do not form 1 Cf. Doflein, 97. ^ See Floderus, 95, and Obst, 99. ^ Cf.^. 349. GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 151. a follicle, but in some forms each o.^^ is accompanied by a singlenurse-cell, attached to its side, with which it floats free in the body-cavity. In Ophryotrodia, where it has been carefully described byKorschelt, the nurse-cell is at first much larger than the Qg^ itself, and contains a large, irregular nucleus, rich in chromatin (Fig. j^).The egg-cell rapidly grows, apparently at the expense of the nurse-cell, which becomes reduced to a mere rudiment attached to one sideof the Q.^g and finally disappears. There can hardly be a doubt, as Korschelt maintains, that the nurse-cell is in some manner con-nected with the elaboration of food for the growing egg-cell; andthe intensely chromaticcharacter of the nucleus iswell worthy of note in thisconnection. Still more in-teresting are the conditionsobserved by Wheeler (96, 97) in Myzostoma, wherethe young Q^g is accom-panied by two nurse-cells, one at either end. Thesecells fuse bodily with the^gg, one

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• bookcentury1900
• bookdecade1900
• bookyear1902
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