JUNE 14, 1912] 
belong specifically to the germ plasm is 
found in Meves’s observation of the so- 
ealled chrondriosomes which he finds 
widely distributed in the tissues of the 
embryo chick and so evenly scattered in 
the cytoplasm of each cell that they are 
somewhat equally allotted to the daughter 
cells in division. That these bodies may 
be concerned in heredity is however hardly 
more than an interesting suggestion. That 
any considerable portion of their material 
is really derived from the male gamete is 
certainly not proven. In sexual reprodue- 
tion they are as yet to be classed with the 
ordinary cytoplasm. That they are, how- 
ever, widely distributed cell organs seems 
probable. Unpublished observations in 
my own laboratory show that they are 
present in the embryonic muscle, connect- 
ive tissue, cartilage and nerve cells of trout 
embryos with the same appearance and ap- 
parently the same relation to the forma- 
tion of muscle and nerve fibrils, ete., which 
has been deseribed by Meves for the chick. 
That similar structures are also present in 
embryonie tissues of plants seems probable 
from the recent preliminary announce- 
ment and figures of Guilliermond showing 
their appearance in the embryonic eells of 
the kernels of the cereal grains thus con- 
firming the still earlier observations of 
Bigaud and Lewitsky. That they are in 
reality anlagen for the cell plastids needs 
further proof, of course, but that we have 
in them an important and widely oceurring 
stage in the differentiation of embryonic 
cytoplasm into the characteristie organs of 
specialized cells in both animals and plants 
is strongly suggested. Their study may be 
expected to throw further light on the 
methods by which the material transmitted 
by the germ cells comes to its expression 
in the structural features of the adult 
tissues. 
Other minor objections are being urged 
SCIENCE 
911 
repeatedly against the doctrine, but in my 
opinion it must be taken as one of the best 
established facts of cytology to-day that 
there is a specific germ plasm’ differen- 
tiated from the general protoplasm of the 
cell, and that this specifie plasm is at least 
carried by and continuously present in the 
stainable materials of the nucleus. From 
the cytological side, evidence has continu- 
ally increased that we have in the chro- 
matin of the nucleus a physical basis of 
heredity in a very specific sense. 
When we turn to the interesting question 
as to how far the laborious and widespread 
cytological studies of the past decade have 
gone toward confirming the earlier cor- 
puscular theories as to the ultimate strue- 
ture of this germ plasm, we are confronted 
for the most part as yet with negative re- 
sults. It can be claimed by no one that 
there is any substantial agreement. among 
students of the cell to-day as to the exist- 
ence even of any visible organized struc- 
ture in the chromosomes themselves. 
Heidenhain is the most effective recent de- 
fender of the theory of an ultramicro- 
scopic organization of the cell and nucleus, 
but his arguments for the existence of a 
bio-system below the grade of the chromo- 
some represented by chromioles and cen- 
trioles has met with no general acceptance. 
As Haecker affirms, there is no agreement 
as to any facts of structure in the chromo- 
somes themselves. The existence of the 
chromioles as specific units has not been 
confirmed. Errera has made it clear that 
bodies of the size of the chromomeres could 
contain only some thousands or less of 
proteid molecules, according to the chem- 
ical evidence, and it is hardly possible that 
an organization of any significance could 
be achieved with so few units. It is not 
impossible that in the chromosomes we 
have reached the ultimate units in the or- 
ganization of the cell, themselves not or- 
