722 Proceedings of the Royal Irish Academy. 



In anotlier form of division, whicli I have observed in these nuclei, 

 a number of (fig. 3) bud-like protuberances are formed on and project 

 from the surface of the large nucleus. These protuberances may swell 

 into a bag-shaped form and be cut off from the parent nucleus, or they 

 may branch and form two such bag-like appendages to the large nucleus, 

 which become cut off from it by the attenuation of the connecting 

 stalk. Each of the fragments thus severed from the parent nucleus 

 has all the appearance of a small nucleus. The number of these 

 fragments so cut off may be considerable, so tbat in the protoplasm 

 round a nucleus, budding in the manner I have described, as many as 

 ten to fifteen of them may be seen. 



Again, in direct division, the nucleus may become ring-shaped 

 (fig 4), and by the gradual attenuation of the annular nucleus in two 

 places it becomes parted into two nuclei. In some cases the ring 

 attenuates in three places and so the nucleus is divided into three 

 nuclei. Fig. 5 furnishes an example of both processes. ^ 



In the simplest form of direct division the giant nucleus elongates 

 and becomes constricted about the middle, it then assumes the shape of 

 an hour-glass, and finally breaks into two fairly equal portions (fig. 13). 



In the smaller nuclei also of the embryo-sac I have noticed irregulari- 

 ties of division. The most interesting of these are those forms of nuclear 

 fission which are intermediate ^ between normal karyokinesis and 

 direct division. In one of these forms before direct division the nuclear 

 thread breaks into a number of shorter pieces and the nucleoli disappear. 

 "Without the nuclear membrane, however, dissolving or the formation 

 of the nuclear plate, the nucleus becomes constricted across the middle 

 so that it appears dumbell-shaped (fig. 6). The connecting piece between 

 the two ends of the dumbell is usually situated more to one side than 

 the other, and beside it in the protoplasm fibres arise, which present 

 the appearance of a normal spindle.^ The fact that even in these 

 forms of direct division, where the nuclear membrane does not 



^ Eing-shaped nuclei and their direct fragmentation are described by W. 

 Flemmiiig (Arch. f. Mikros. Anat., 37, 1889) as occurring in the leucocytes of 

 the Salamander ; cf. also Arnold (Archiv f. Mikrosk. Anatomie, 1889) and 

 Goppert in the same journal, 1891. 



* W. Flemming {loc. cit.) says: " Ein bestimmter Unterschied z'waschen 

 directer und indii'ecter Fragmentirung will mir iiberhaupt nicht recht durchfiihrbar 

 erscheinen." 



Hess also (Ziegler's Beitrage z. pathol. Anat. u. z. allg. Pathol., Bd. viii.) 

 found nuclear figures in the spleen of the mouse, which he regards as intermediate 

 forms between direct division and mitosis. 



^ W. Flemming {loc. cit.) found that the centrosomes lay usually at the one side 

 of the narrow connecting filaments between the nuclei undergoing direct division. 



