ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 89 



auimal and vegetable cells. His own observations lead him to tbe 

 conclusion tliat tbe different elements of the active nucleus are deve- 

 loped out of distinct portions of the nucleus when in a state of 

 rest. 



Structure and Formation of the Cell-Nucleus.* — The result of 

 a series of observations on this subject liy L. Juranyi has led him to 

 very much the same conclusions as those of Flemming | and the later 

 ones of Strasburger. The nucleus is composed of threads and a 

 nucleolus. The former consists of two substances, a fundamental 

 substance (matrix) which is not coloured, and corpuscles imbedded in 

 it which take pigment. These increase and multiply, and finally 

 coalesce; the threads then take the pigment along their whole length, 

 and the nucleolus disappears. In the Cycadeee the nucleoli are very 

 large, and consist of a central strongly refringent corpuscle and a 

 thick less refringent envelope, the latter being much less strongly 

 developed in other plants. After the disappearance of the nucleolus 

 the thread becomes gradually thicker, but one or sometimes two 

 strongly refringent particles can be seen on the surface of the nucleus, 

 resembling the nucleoli, but not receptive to pigment. After the 

 threads have become much thicker and shorter they break up, the 

 fragments either becoming applied to the wall, or touching it with 

 one end, the rest dipping into the nuclear fluid. The protoplasm 

 now takes the place of the nuclear fluid, and forces the fragments of 

 the threads towards the plane of division, thus forming the nuclear 

 plate, and the nucleus therefore consists originally of two halves. 

 The fragments mostly take the form of a C or a U, their convex side 

 facing the division-plane. The nuclear spindle now makes its 

 appearance, its fibres being no doubt formed from the cell-protoplasm, 

 as can clearly be made out in the Cycadeee. The elements of the 

 nuclear plate are always fragments of filaments, but the structure of 

 the plate may vary according as its elements remain distinct, approach 

 one another, or coalesce in consequence of the action of reagents. Re- 

 agents affect the form of the fragments so much that the plates of 

 sister-cells may be composed of elements of quite different form, and 

 even the elements of the same plate may difter from one another in 

 this respect. The two halves of the nuclear plate, now fully developed, 

 move to the pole of the nuclear spindle, the fibres of the spindle 

 remaining behind and constituting from this time the uniting-threads. 

 During this movement the fragments of the threads take up such a 

 position that their concave surface faces the division-plane. After the 

 elements of the plate have reached the pole of the spindle, they appear 

 scarcely to move away from the uniting-threads. While this is going 

 on, granular protoplasm is formed round them, which incloses both 

 the fragments of the threads and a portion of the fluid between the 

 uniting-threads and the elements of the plate, and thus is produced 

 the vacuole in which the elements of the new nucleus lie free. The 



* Ungar. Acad. Wiss. Buda-Pest, Oct. 16, 1882. Sec Bot. Centralbl., xii. 

 (1882) p. 215. 



t See this Journal, i. (1881) xi. 11. 



