STUDIES ON CHROMOSOMES 73 



would be difficult to disprove this in ordinary cases; but fortun- 

 ately 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 cogency 

 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 



