THE PHYSICAL BASIS OF HEREDITY. ISI 
magnification, it is found to consist essentially of a 
delicate network or system of threads, the “linin net- 
work,” bearing granules of a substance rich in phos- 
phorus, which, from its affinity for certain staining 
fluids, has been termed “chromatin,” One or more 
rounded structures, behaving in certain definite ways 
toward reagents, may also be found in the nucleus. 
These, the “nucleoli,” are probably not always of the 
same nature in different cells, and their significance is 
at present much less clearly understood than is the case 
with the other nuclear structures. Filling the meshes 
of the nuclear network is found a clear semi-fluid ma- 
terial, the “ karyolymph,” and a more or less clearly de- 
fined wall, the nuclear membrane, incloses the nuclear 
substances and separates them from the cytoplasm. 
In 1876 Van Beneden announced the discovery of a 
minute rounded body at the poles of the spindle in the 
dividing eggs of Dicyemids, which has since been found 
in nearly all kinds of animal cells, both in division and 
in the “resting condition,” and may probably be re- 
garded as of universal occurrence, so far at least as 
animal cells are concerned. In plants, however, it has 
thus far been identified with certainty in but few forms. 
To this structure Boveri, in 1888, gave 
the name of “centrosome,” and showed 
it to be a cell organ of probably constant occurrence 
and of the greatest significance in cell multiplication. 
It often lies in a more or less specialized area of the 
cytoplasm, the ‘attraction sphere,” or “archoplasm,” 
near the nucleus, but in some forms it is doubtless with- 
out any such surrounding structure. 
The foregoing paragraphs must be taken merely as 
the briefest outline of cell structure. It would far ex- 
ceed the limits of this article to attempt to discuss the 
finer detail of the subject, or to enter upon the many 
The centrosome. 
