Nuclear Division in the Hcpaticae . 509 
would seem that in this plant, the centrosomes, if present, are 
also intra-nuclear. Their particular location depends on the 
arrangement and position of the systems of forces operating 
in the cell. I have already mentioned the fact that cases are 
known in animal cells, and particularly in those mitoses 
which accompany the maturation of the ovum, in which no 
centrosome presides over the process of karyokinesis by 
which the polar bodies are cut off. Brauer 1 has described 
such a case in Artemia , and when a centrosome is finally 
summoned into existence, it seems to arise as the result of 
a mere condensation of protoplasm. 
So long as it was believed that the male and female 
centrosomes generally fused during fertilization, it was very 
natural (though not necessary) that considerable importance 
should be attached to these bodies, but we now know that 
as regards animals, this fusion does not take place, and that 
Fobs statements were based upon defective preparations. 
Sometimes the centrosome connected with the ovum 2 , oftener 
that associated with the sperm nucleus 3 , alone persists, whilst 
the other one disintegrates and becomes lost, merged in the 
general cytoplasm. Another factor which enhanced the value 
of the centrosome depended on the discovery that during 
nuclear division these bodies also divide, and further that, 
in some cells at any rate, they persist through the interval 
which elapses between two successive mitoses. But in con- 
nexion with the latter point, it may be remarked that the 
divisions in these instances often succeed each other with 
such rapidity that the cell has not, in the interim, settled 
down to a state of rest. In other cases again, such as in 
certain cells described by Heidenhain 4 , it is not clear whether 
1 Zur Kentniss d. parthenogenet. sich entw. Eies v. Artemia salina. Arch. f. 
Mikr. Anat., Bd. XLIII. 
2 Wheeler, The Behaviour of the Centrosomes in the fertilized egg of Myzostoma 
glabrum . Journ. of Morphology, Vol. x. 
3 Julin, Structure et Developpement des glandes sexuelles . . . chez Styelopsis 
grossularia. Bull. Sci. de la France et de la Belgique, T. XXV, p. 56 of the 
separate copy. 
4 Ueber Kern 11. Protoplasma. Festschr. fiir A. v. Kolliker, 1892. 
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