STUDIES ON CILIATED CELLS 259 



nuclei of the ciliated pharyngeal cells is smooth or shows at the 

 most some irregularities. At the beginning of the nuclear con- 

 striction the nuclear membrane is characteristically thrown into 

 folds, this is most marked in Rana temporaria. The cleavage- 

 plane of the nucleus is either vertical (figs. 42, 49) or oblique, or 

 even horizontal (fig. 44). The furrow formed by a pushing in 

 of the nuclear membrane appears, in Rana esculenta, as two par- 

 allel straight lines (fig. 42), but in Rana temporaria as zigzag 

 lines which can be made out only by careful focussing (fig. 51). 

 Between the structure of the amitotic dividing nucleus and that 

 of the normal one there are no noteworthy differences, as will 

 be seen in my figures. The daughter nuclei are at first closely 

 apposed by their divided faces; later on, they are gradually 

 separated from each other (figs. 43, 52). I have observed in 

 Bufo a curious phenomenon in the behavior of the centrosome in 

 the amitotic process : the ciliated cell in the pharyngeal epithelium 

 of this animal, as already mentioned, contains a bigranulated 

 centrosome lying above the nucleus (fig. 49, the cell to the left). 

 With the separation of the dividing nuclei from each other, each 

 of the granules accompanies each daughter-nucleus (fig. 49, the 

 cell to the right), a fact which indicates that the centrosome is 

 not entirely independent of amitotic nuclear division. 



Cell-division follows nuclear division. Since the cytoplasmic 

 fission always takes place along its longer axis of the cell, being 

 inaugurated either at the upper end (fig. 45) or at the lower 

 (fig. 48), it must be thought that the superposed nuclei, as it 

 often occurs, undergo locomotion before the cell-division sets 

 in. In the amitotic process there are no visible structural 

 changes of the cytoplasm, the nucleus, or of the ciliary appara- 

 tus, except that the two former increase more or less in volume. 



3. The gall-duct of Rana temporaria. Ciliated cells with two 

 closely appHed nuclei occur, though not frequently, in the bile- 

 duct epithelium. The process of cell-cleavage, however, was 

 not observed. 



4. The oviduct of Rana temporaria and esculenta. In the ovi- 

 ducal epithelium are large ciliated cells with two nuclei (fig. 

 64), which cannot be interpreted except as having been pro- 



