146 
R. T. Young 
fication of the nuclear reticulum and bounds the lighter area which ordi- 
narily surrounds the »nucleolus« or »nucleoli« and eomposes the major 
part of the nucleus. Sometimes there is no definite chromatin present 
but merelv a lighter part of the general granulär reticulum of the cell 
which is bounded by an indefinite membrane. Such nuclei represent 
probably developmental stages. Usually there is but a single chief »nuc- 
leolus« but occasionally there are two or three such, and in a few cases 
definite »nucleoli« are lacking, the nucleus consisting of a chromatic 
reticulum the outer part of which forms the membrane. Frequently 
also there are darkly staining granulös lying on the membrane and sug- 
gesting a common origin for both as previously suggested by me (1. c., 
p. 239). 
In material stained in methyl green and fuchsin the »nucleoli« stain 
blue, while the membranes and cytoplasm are typically pink. In those 
cases, however, in which the nucleus stains heavily in the green, the 
membrane takes a dark blue or purple cast. Tliis evidence indicates the 
chromatic nature of the »nucleolus«, and the achromatic character of the 
nuclear membrane. It does not, howtver, show that these are funda- 
mentally different, or that they may not have had a common origin, as 
I have suggested above. In the adult nucleus, however, the membrane 
and the »nucleoli« have apparently become differentiated chemically 
as well as physically from each otlier. 
Thysanosoma actinoides. 
(Figs. 3 and 4.) 
Cytological conditions in this worin are similar to those dcseribcd 
above in Moniezia. While large massts of cytog nie protoplasm are 
wanting there are many smaller masses of granulär protoplasm scatter d 
thru the parenchyma syncitium. In th se occur granul s unsurround d 
by membranes which stain intenselyin th; chromatin sta.n, and are I 
believe small chromatin elennnts, the anlag n of futur nucl i. In ad- 
dition to solitary »nucleoli« without membran s nuclei an found con- 
sisting of one or more small »nucleoli« surroundcd by v ry indistinct 
membranes. Careful focussing and examination of adjacent sections 
show that these »nucleoli« are not in close proximity to others. Absolute 
proof that they have not beeil given off by pre-existent nuclei and 
wandered into their definitive stations, there to endose themselves in 
membranes and become adult nuclei, is, however, difficult to obtain. 
There is indeed in a few cases some evidence of fission or budding of 
