550 Lewis. — The Behaviour of the Chromosomes 
spirems previous to synapsis, and asserts that the synaptic phase does not 
consist in the uniting of somatic chromosomes side by side. This view 
maintains that the chromomeres and the linin threads connecting them 
never become arranged in parallel rows, and that the chromatic content 
of the nucleus approaches the synaptic condition rather in the form of 
a reticulum of single chromomeres connected by single strands of linin. 
This chromatin reticulum becomes converted during synapsis into an 
endless spirem, which undergoes longitudinal fission shortly after it is 
formed, and then segments transversely into the chromosomes. The chromo- 
somes cpnsist of two pieces of the spirem which have either come together 
after cross-segmentation or were not disassociated, but remained together 
at the time of segmentation. These pieces become variously oriented 
toward each other, and so give rise to the heterotype forms typical of this 
mitosis, a condition which harmonizes perfectly with the observed facts in 
both Pinus and Thuja. 
It will be seen, therefore, that these two views agree perfectly as to the 
nature of the bivalent chromosomes, but differ widely as to their manner of 
origin from the resting nucleus. It seems then that the questions of the 
origin and ultimate destiny of chromosomes cannot be regarded as finally 
and definitely settled. In this connexion one must not forget to take into 
account that, in dealing with a phenomenon of such wide occurrence as that 
of mitotic division, it is strongly probable that the process will be found to 
be uniform in regard to all of its essentials, although differing in minor 
details, else how shall we explain its significance ? 
The Idioplasmic Theory of Heredity. 
In speaking of the chromomeres as the bearers of hereditary characters, 
it is, of course, implied that these bodies are responsible only by their 
influence on the less stable cytoplasm. No attempt will be made at this 
time to enter into a discussion of the various ways in which the idioplasmic 
theory, first proposed by Nagelei, has been developed. In some form or 
other it has held the centre of thought among students of heredity for the 
past thirty years. That the idioplasm, which is identified by all investigators 
with the chromatin, constitutes the entire mechanism of heredity has not 
been accepted by all investigators, and recent work is causing a growing 
belief that the cytoplasm of the egg at least is fundamentally concerned 
with the transmission of characters. 
In its extreme form the idioplasmic theory assumes that every organism 
may be analysed into a certain definite number of unit characters, and that 
in the cells of the organism a number of material primordia may be found 
which correspond with such units. It is of course needless to say that such 
a condition has not been shown to exist, although it is known that many 
characters behave as distinct units. ‘ It is known that a definite kind of 
