ACCESSORY CHROMOSOME IN ANASA TRISTIS. 123 



chromosomes are clearly defined a transverse division for each 

 chromosome can be plainly demonstrated by one photograph. 

 In many other cells, however, it can be as clearly determined 

 that the " eccentric " chromosome divides longitudinally while 

 all the others divide transversely. It may be stated, as a rule, 

 that the "eccentric" chromosome divides longitudinally, though 

 many exceptions can be demonstrated. 



Tlic Lagging Chromosome of the First Division. At the late 

 anaphase or early telophase of many of the first divisions, it can 

 be demonstrated that one of the chromosomes has divided at a 

 later period than the others. It may be seen between the two 

 poles in all stages of separation --sometimes the entire bivalent 

 will be between the poles, its two univalent halves having just 

 separated or one univalent may have reached one pole while the 

 other half still lies midway between the poles. We have several 

 photographs in which a lagging chromosome is shown while all 

 the other chromosomes can be counted, thus an error in inter- 

 pretation is quite impossible. As a rule this lagging chromosome 

 appears to be the "eccentric" chromosome, though it cannot be 

 demonstrated that it is invariably the same chromosome which 

 lags in division. We have not found this phenomenon with 

 sufficient frequency to justify our interpreting it as a constant 

 feature of this division. We think the condition exceptional, 

 though not necessarily pathological. 



The Lagging Chromosome of the Second Division. The second 

 division shows a phenomenon which appears to us to be the 

 equivalent of the one just described for the first division. It is 

 more frequently found for the second spindle than for the first 

 and much more difficult to interpret, as these spindles are so 

 exceedingly small and the chromosomes so closely crowded 

 together, that cases are rarely found in which all the chromo- 

 somes are in evidence and the true value of the lagging chromo- 

 some can be safely interpreted. We have a few photographs 

 which we think throw some light upon this point. All the 

 chromosomes at each pole are demonstrated and the lagging 

 chromosome lying midway between the poles, in several cases 

 shows a distinct transverse constriction. In one preparation the 

 two halves have separated, and in another the two halves have 



