. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. J. F. have been made on Ascaris eggs by Auerbach ('74) ; on am- phibian eggs by Pfluger ('84), Roux ('85, '93), Born ('93, '94), O. Hertwig ('93) ; on echinoderm eggs by Driesch ('92, '93, '95), Morgan ('93), Ziegler ('94) ; on ctenophore eggs by Ziegler ('94); and on Nereis eggs by Wilson ('95). These experi- ments show that if the egg is pressed more on certain sides than on others, as when it is pressed between two plates of glass and forced to assume a flattened shape, that the direction of the cleavage spind
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. J. F. have been made on Ascaris eggs by Auerbach ('74) ; on am- phibian eggs by Pfluger ('84), Roux ('85, '93), Born ('93, '94), O. Hertwig ('93) ; on echinoderm eggs by Driesch ('92, '93, '95), Morgan ('93), Ziegler ('94) ; on ctenophore eggs by Ziegler ('94); and on Nereis eggs by Wilson ('95). These experi- ments show that if the egg is pressed more on certain sides than on others, as when it is pressed between two plates of glass and forced to assume a flattened shape, that the direction of the cleavage spindles (and consequently cleavage fur- rows) will be affected. Hertwig formu- lated the law that the spindle lies in the longest axis of the protoplasmic mass of the cell. This rule probably applies in the majority of cases, but there may be some exceptions, and there are evidently other and unknown factors which enter into the polar differentiation of the cell. Bigelow found in Lepas ('02) that the polarity of the egg was not affected by the oval form of the rigid chorion. The principal axis of the egg coincided with the long axis when the chorion was se- creted and during the prophase of the first cleavage spindle the egg rotated through a right angle so that the first cleavage spindle was made to coincide with the long axis of the egg determined by the form of the chorion, and the principal or primary axis was perpen- dicular to it. I found a similar condition in Endactylina nigra Wilson. If the egg string of this copepod be placed in sea water under the micro- scope during the first cleavage stage, the majority of the eggs will have their spindle axes, or in case the division is complete, common cell axis, nearly in the same plane. Often, however, some of these axes are considerably inclined to this plane as is shown in Fig. 4, A. If the egg string be pressed between slide and cover glass the above axes will rotate sufficiently to bring them all in a plane midway FIG. 4. Egg s
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
