STUDIES ON CHROMOSOMES 
73 
would be difficult to disprove this in ordinary cases ; but fortun- 
ateh^ Boveri's studies on Ascaris ( '09) have shown beyond all doubt 
that in this form there is no constancy in the original position of 
the prophase chromosomes, the only definite order being shown in 
the close agreement of each pair of daughter-cells. The position 
of the prophase chromosomes as Boveri shows with great cogenc}^ 
is here a consequence of the position in which they entered the nu- 
cleus in the preceding telophases; as the latter position is itself due 
to causes (which may be quite fortuitous) that determine the posi- 
tion of the preceding metaphase chromosomes. 
The facts support no less directly and strongly the conclusion 
that the chromosomes differ among themselves in a definite way 
in respect to their behavior, and hence in respect to their functional 
significance. The differences seen in the maturation-process have 
thus far taught us nothing whatever in regard to the individual 
physiological meaning of the chromosomes, in heredity or other- 
wise, and they are not to be compared in value with the results of 
direct experiment, such as those carried out by Boveri ('07) in 
dispermic sea-urchin eggs. It is nevertheless of great interest that 
the results from these different sources should be in harmony. In 
my preceding paper I have called attention especially to the sig- 
nificance of the couplings of the chromosomes, pointing out that 
these certainly do not depend upon the size of the chromosomes 
(though those which couple in synapsis are in fact equal members 
of a pair save in certain special cases) nor can they, apparently, 
depend upon the achromatic mechanism. The various combina- 
tions in Metapodius seem to arise simply by the addition or sub- 
traction of certain chromosomes without alteration of the achro- 
matic elements; yet in the resulting new combinations the chro- 
mosomes still behave each according to its kind, and (as previously 
indicated) irrespective of their size. We seem thus driven to 
accept the view that the chromosomes are physico-chemically dif- 
ferent, with all the consequences which such a view may involve. 
The cogency of the evidence in favor of the qualitative differ- 
ences of the chromosomes brought forward in Boveri's masterly 
work must be generally recognized, as has recently been admitted 
even by Driesch ('09) who formerly endeavored to find a different 
