MULTIPLE CHROMOSOMES 549 



subject to conditions within the system of which the chromosomes 

 are a part. The chi'omosomes are temporary and variable or- 

 ganizations of the chromatin, which form in the prophase and 

 dissolve in the telophase. Variations in size of chromosomes 

 are within the limits of observational error and are of the order 

 of size variations in the droplets of an emulsion. Correspond- 

 ence in size between chromosomes and nucleus finds its explana- 

 tion in the physical condition of adsorption. The fact that 

 chromosomes shorten proportionally to their original length 

 shows they are homogeneous and indicates the identity of all 

 the chromosomes in a mitosis. The previous history of the 

 chromosomes in a line of cells can have no effect upon later 

 generations because there is no continuity. Definite or specific 

 organization is lacking and there is no perpetuation of a series 

 through reproduction of individual chromosomes. All expla- 

 nations of variations in number (called 'sub hypotheses') are 

 declared to be untenable upon 'accurate examination' and cer- 

 tain determination of numbers in sections is stated to be im- 

 possible. As is customary with critics of this type, Delia Valle, 

 after decrying the spirit and purpose of those who do not agi'ee 

 with him, proceeds to attack their methods and declares that 

 only his own technique yields infallible results. Sections can 

 not give accurate enumerations of chromosomes, and only 

 counts made upon stretched membranes are of value. Having 

 thus put out of count the bulk of the work already done, he 

 next makes a comparatively hmited number of observations 

 upon one type of material and arrives at the ultimate general 

 conclusion that chromosomes are fluid crystals. With this 

 solution of the problem accomphshed, all minor questions are 

 easily settled, because upon this major premise that chromo- 

 somes are fluid crystals and subject to all the laws known to 

 pertain to such physical aggregates, certain variations of num- 

 ber, size, form and behavior must exist. I should like now to 

 consider some of these assertions in the hght of work known to 

 me personally, first pointing out that all instances of order and 

 system under varying conditions are direct evidence against his 

 position. 



