INTRODUCTION 7 
ing’ nucleus a network of fibers may be observed 
similar to the spongioplasm in the cytoplasm; 
these consist of a substance named linin because it 
usually occurs in threads (Fig. 1, 1). Distributed 
along the linin fibers are granules of a substance which 
stains deeply with certain dyes, and for this reason is 
known as chromatin (ch). These chromatin gran- 
ules may unite to form larger spherical masses, the 
karyosomes or chromatin-nucleoli (/), and during 
mitotic nuclear division constitute the chromosomes 
(Fig. 3, C). In many cells one or more bodies 
resembling the karyosomes somewhat, but differing 
from them chemically and physiologically, are pres- 
ent; these are the true nucleoli or plasmosomes 
(Fig. 1, pl). Embedded in the cytoplasm near 
the nucleus may often be seen a granular body, the 
centrosome (c), which is thought to be of great 
importance during mitotic cell division. The pro- 
toplasm surrounding the centrosome is usually a 
differentiated zone, the attraction-sphere (as), con- 
sisting of archoplasm. The chromatin which may be 
seen in the cytoplasm of certain cells is as a rule 
in the form of granules called chromidia (er). Cer- 
tain other cytoplasmic inclusions that have attracted 
considerable attention within the past fifteen years 
exist as granules, chains, or threads, and are known as 
mitochondria, chondriosomes, plastosomes, etc. (m). 
Various sorts of plastids (p), such as chloroplastids 
and amyloplastids, may be present, besides a varying 
number of solid or liquid substances, collectively 
designated as metaplasm (me) or paraplasm, which 
