138 BULLETIN OF THE 



division might take place transversely to the axis, this result could still 

 be attained bv a rotation of the nucleus, even when the tendency was for 

 the nucleus to divide at right angles to the previous division. It is 

 obvious that rotation would occasionally be apparent, provided it took 

 place soon after division, and previous to the absorption of the proximal 

 end of the connecting filament. I examined a large number of prepara- 

 tions to find evidence of rotation, but I must admit that the evidence 

 was slight, and hardly sufficient to establish the hypothesis which I had 

 formulated. It is therefore put forth provisionally, in the hope that it 

 may lead to further investigations in this line. 



The most striking instance of rotation was found in one of the quadri- 

 nucleate cells (Fig. 33, nuclei a and h). It is evident that three nuclear 

 divisions have taken place without any division of the cell, producing 

 two, three, and four nuclei. The arrangement of nuclei makes it rea- 

 sonably certain that the loicer pair arose by division of one, and the 

 tipper pair by division of the other nucleus of the binuclear stage. 

 Only under this supposition could the daughter nuclei of that stage 

 have had the normal arrangement, to which all the neighboring cells 

 rigidly conform. "SVe further find, that, while the upper pair of nuclei 

 has arisen by a division in the long axis of the cell, the lower pair has 

 been produced by division in the transverse axis, and therefore in con- 

 formity with the law previously stated (p. 136). One nucleus of each 

 pair (a and 6) retains a remnant of the connecting filament, which is 

 directed, not toward the sister nucleus, but to a point 90° distant from 

 it. This condition could have been brought about only by rotation of 

 the nuclei, which in both cases has been through an arc of 90°. 



In the serosse from older embryos, the daughter nuclei almost inva- 

 riably recede from each other in the course of division. The amount 

 of recession is governed by the length of the cell (Fig. 15). In the 

 younger membranes, as already stated, the constriction is deep and 

 narrow, so that the nuclei not infrequently lie very near together 

 (Fig. 13). In these young membranes, however, the nuclei are larger, 

 and the cells are usually smaller, than in the old membranes. Since, 

 moreover, the large binucleate cells of young membranes almost always 

 have their nuclei symmetrically placed at the ends, it is probable that 

 the nuclei gradually move apart after division, as the cell increases in 

 size. 



It will be seen that my interpretation of the primary cause of the 

 division of these nuclei agrees in part with the hypothesis advanced by 

 Chun ('90) for the explanation of amitotic division in general. This is. 



