ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
43 
daughter-cells. (4) The existence during the synapsis of a peculiar 
evolution among the constituents of the attraction-sphere, whereby the 
eentrosomes are brought to its exterior surface. (5) The repetition of 
the process in a more pronounced manner, so that a short flagellum is 
protruded from the eentrosomes through the membrane of the cell. 
(6) The origin of the long whiplash tail of the spermatozoon in a similar 
manner, after a corresponding metamorphosis of the sphere during the 
formation of the flnal cellular generation. In the comparative sketch 
with which Mr. Moore concludes his memoir, he points out that the re- 
productive cycles of animals and plants correspond, not only in the 
number of the chromosomes typical of the somatic cells of any species 
being halved, but also in the successive and complex phases by which 
their numerical reduction is brought about, as well as in the type of 
modification which the post-synaptic cellular generations may undergo. 
Whatever the synapsis may eventually turn out to be, it is evidently a 
cellular metamorphosis of a profoundly fundamental character, which 
would appear to have been acquired before the animal and vegetable 
ancestry went apart, and to have existed ever since. 
£. Histology. 
Centrosome and Sphere in the Spinal Ganglion-Cells of the Frog.* 
— Prof. M. v. Lenhossek has succeeded for the first time in securely 
proving the presence of a centrosome in nerve-cells which have long 
since ceased to divide. The plasma is disposed concentrically, not 
around the nucleus, but around an almost central point — the centrosome. 
This is a very important observation, and strengthens the position of 
the centrosome. It occurred regularly, not in all the spinal ganglion- 
cells, however, but in the second smallest. 
The cell-substance consists of two distinct zones, ectoplasmic and 
endoplasmic. The outer has a clear matrix and coarse flakes in longitu- 
dinal rows parallel to the surface. These are probably thickenings in 
the honeycomb-like structure of the plasma. In the endoplasm there 
are small granules in concentric lines. The two zones differ in their 
staining reactions, and in other w'ays ; in short, there are two distinct 
kinds of microsomes. 
The centrosome lies in the middle of a central disc ; it is an aggre- 
gate of minute granules, and there is no doubt as to its nature. But 
the central disc corresponds only to the medullary layer of van Beneden’s 
attraction-sphere, and may perhaps be called a centrosphere by way of 
distinction, though this is a new use. 
The centrosome always lies in the main portion of the cell-substance, 
in the middle of the endoplasm, never in the immediate neighbourhood 
of the nucleus. The nucleus is eccentric, and if the cell is divided at 
the level of the centrosome, it is seen that the part of the cell in which 
the nucleus lies is larger than that in which the centrosome lies. Len- 
hossek’s theory is that the centrosome would have exactly equal masses on 
each side of it, if the nucleus were not there. 
No eentrosomes were found in the spinal ganglia of cat and dog, and 
in these cases the nucleus is quite central. Perhaps the dynamic or 
* Arch. f. Mikr. Anat., xlvi. (1895) pp. 345-69 (2 pis.). 
