342 BULLETIN OF THE 



(3.) Nuclei of like size, but more elongated, the two ends consistin<y 

 of two saucer-shaped structures with their cavities facing, and the inter- 

 vening portion occupied by numerous filaments differing in thickness 

 stretched between these two structures. The " saucers " appeared at 

 times as though composed of radiating filaments, at others as though 

 made up of a nearly homogeneous, lustrous substance. The equatorial 

 disk is no longer visible. The distance between the saucers is now 

 more, now less. The connecting fibres rupture successively. The 

 " saucers " become flattened into disks, and appear either as a mosaic of 

 rods or else homogeneous. The disks become thicker and rounded, and 

 acquire vacuolar cavities in which nucleoli appear. They now nearly 

 resemble the neighboring nuclei. 



Accompanying changes in the shape of the cell and its constriction 

 ultimately end in cell-division, the nuclei, at first close to each other, 

 sometimes appearing to be still joined by fine filaments. They subse- 

 quently move apart, and the cells, like those which surround them, 

 become polygonal. 



Mayzel ventures the statement that, at the free edge of the regenerat- 

 ing patch of epithelium, the nuclei are without doubt formed [not by 

 division but] by differentiation out of the protoplasm.* 



The observations of Ed. van Beneden ('75) on ectoderm cells of the 

 rabbit embryo are to be found at pp. 302, 303. 



Semper (75^ pp. 361, 362, Taf. XIX. Fig. 29, x), among the " Ureier " 

 of Acanthus, found some whose nuclei were smaller than usual and ap- 

 peared to be composed of small granules often radially arranged about 

 a centre. Such nuclei are more deeply stained in hjematoxylin than 

 the ordinary nuclei. Semper is inclined to connect them with the pro- 

 cess of cell division, especially in view of their close similarity to the 

 phenomena accompanying segmentation, as shown by Biitschli, Auer- 

 bach, and Flemming. 



EwETSKY ('75) seems, according to Strasburger ('76, p. 228), to have 

 figured something of the phenomena of nuclear division. I have not 

 been able to consult his paper. 



Besides his study of the blastoderm cells of insects, the results of 

 which have already been given (p. 320), Butschli ('76, pp. 249 - 2G2) 

 extended his investigations to an examination of cell and nuclear 

 division in the germ cells of the spermatozoa of Blatta, and in the 

 blood-corpuscles of the fowl, the frog, and Triton. The more important 



* " Dass die Kerne ohne Zweifel durch Differenzirang aus dem Protoplasma sich 

 frei bilden.'' 



