May 17, 1912] 
during the events immediately preceding 
the metaphase of the reduction division, 
eytologists are somewhat divided on mat- 
ters of fact. They are in essential agree- 
ment so far as the genetic continuity of 
the chromosomes is concerned, 7. e., they 
believe that each chromosome is directly 
descended from a previous one. There are 
cases, however, where the propagation of 
the chromosomes is not a simple matter of 
division in which all the substance of the 
old body passes directly into the two new 
ones formed from it by division. 
The manner of formation of bivalent 
chromosomes in the early stages of the 
reduction division is still a matter of dis- 
pute, as is also the possibility or probabil- 
ity of exchange of substance between syn- 
aptic mates. A review of the work on this 
subject would be highly interesting, but 
would extend this paper beyond all reason- 
able limits. 
Recent work has shown that many chro- 
mosomes are really compound bodies, and 
that what we have regarded as independent 
chromosomes are, in some cases at least, 
really groups of chromosomes. This fact 
may have an important bearing on par- 
tial or even complete correlation between 
hereditary characters, as well as the fact 
that in some species more Mendelian pairs 
have been demonstrated than there are 
pairs of chromosomes. 
A third type of investigations relating to 
heredity is the study of the chemical proc- 
esses concerned in development. A great 
deal of the work of the physiological chem- 
ist has a bearing on this subject, though 
not instituted directly for this purpose. 
This study has led to the conclusion, as 
Guyer states, that at least a principal 
function of the chromatin is the production 
of enzymes which, by their regulating ef- 
fects on metabolic processes, produce im- 
portant effects in the development of the 
SCIENCE 
759 
organism. Recently Gortner, of the Car- 
negie Institution, and Miss Wheldale, of 
Cambridge University, have attempted to 
work out the chemistry of certain of the 
pigments, with important results. For in- 
stance, Gortner has shown that, in the 
potato beetle, oxidizing enzymes are gen- 
erally present in the body, while chro- 
mogen, which these enzymes convert into 
pigment, is produced locally in the integu- 
ment in small quantity, and only in those 
locations where the characteristic pigment 
spots occur. One of our own members, 
Dr. Bartlett, is now doing some interesting 
work on the chemistry of anthocyan, and 
has become greatly interested in this phase 
of heredity investigations. Such investi- 
gations relate, of course, to the manner in 
which the hereditary characters make their 
appearance in development, not to the 
transmission of these characters. 
This phase of heredity investigations is, 
as yet, only in its infancy. It is, however, 
one of the most important at the present 
time, for we can not go a great deal further 
in the interpretation of the phenomena of 
heredity until we know more of the chem- 
ical processes involved in the development 
of a complex organism from the fertilized 
egg. 
Lastly, we come to the study, by experi- 
mental cross-breeding, of the behavior in 
inheritance of the various characters which 
distinguish nearly related organisms from 
each other. If relative importance were to 
be judged solely by the amount of data 
accumulated, this would be by far the most 
important phase of the subject before us. 
Here we have a plethora of fact and a 
dearth of meaning. We have now reached 
a point in the study of Mendelian inherit- 
ance where satisfactory interpretation of 
fact is quite as important as the collection 
of more facts. We need stimulating the- 
ories that will point out new directions for 
