MULTIPLE CHROMOSOMES 571 



was this circumstance, of which he had detailed knowledge, that 

 led Robertson to Ibelieve that loops are unusual. 



The form of the chromosome is conceived by Delia Valle to be 

 uniformly that of a rod with rounded ends. Such is frequently 

 the shape of metaphase chromosomes, particularly in the dip- 

 loid condition, but no one who has studied the complicated 

 changes through which the members of the haploid series pass 

 at the synaptic period, could entertain the simple conception 

 of a homogeneous rod spontaneously dividing along its length, 

 advocated by this author. The most remarkable and striking 

 phenomena of biology are entirely ignored by this explanation. 

 Precision of organization, shown byWenrich to extend to the 

 limit of our observational powers, is entirely disregarded by the 

 gross conception of a formed and homogeneous rod clea\'ing hke 

 an unorganized colloid mass. The extensive and significant 

 changes of the prophase, when the division actually occurs, re- 

 ceive no recognition in this crude explanation of chromosome 

 di\dsion. The form of the chromosome . is a much more in- 

 volved question than would appear from the statement of the 

 case by Delia Valle. 



5. Chromosome behavior 



Of very great importance for the theory of chromosome in- 

 dividuality is the beha\dor of the elements united into mul- 

 tiples. If the chromosomes are merely colloid masses — products 

 of the cell — it would not be expected that they should exhibit 

 any differential characters. The very fact that such differences 

 of behavior exist is a disproof of all theories which postulate 

 complete loss of identity and reformation of chromosomes at 

 each mitosis. Unless there is continuity of substance there 

 can not be continuity of organization, because we know of no 

 organization independent of material basis. Besides, such per- 

 sistence of structure and substance is observable. As indicat- 

 ing the high degree of this specificity of chromosome characters, 

 the multiples are of much value, especially when they involve 

 the accessory chromosome. If all the elements of a mitosis are 



