226 KATHARINE FOOT AND E. C. STROBELL. 



ents arise by the omission of a transverse division of a spireme, 

 rather than by a conjugation of univalents. We believe that the 

 evidence in Euschistus is opposed to the interpretation that the 

 chromosomes first appear as univalents and later conjugate, either 

 longitudinally or end to end. We believe, rather, that there is a 

 tendency to form a continuous spireme, because we find cases in 

 which very long, thin, unbroken threads are present, and a few 

 examples of this kind outweigh as evidence, a large number of 

 cases where we find the threads broken into small pieces. These 

 delicate threads could easily be broken by the technique, for after 

 pricking, the germinal vesicles flatten and dry on the slide^and 

 this disturbance, combined with the shrinkage of drying, could 

 easily account for the rarity of the cases in which the long thin 

 threads remain unbroken. 



In Photo 24 we see this tendency to the formation of a spireme 

 -a few of the threads can be traced certainly too far to justify 

 any assumption that they are univalent or even bivalent chromo- 

 somes. A long unbroken thread is also demonstrated in Photos 

 23, 28 and 29. 



Tellyesniczky ('07) claims that the long thin chromatic 

 threads do not become shorter and thicker by contraction. He 

 thinks rather this is accomplished by a flowing together and 

 change of place of the substance of which the thread is composed. 

 He says, there is a continual disintegration and rebuilding of the 

 threads and the new structure is formed at the expense of the old. 



We believe this is not the case in Ensc/iistiis. For example, it 

 seems reasonable to interpret the chromosomes of Photo 30 as 

 due to contraction of long thin bivalents (as shown in Photo 25), 

 rather than to regard them as entirely new formations. Such a 

 detail as this is interesting, but it seems to us only incidental to the 

 all-important question, do the chromosomes retain their individu- 

 ality throughout the rest stages do they differ in this particular 

 from other structures of the cell the centrosome the aster - 

 the spindle the nucleolus, etc. These elements return at each 

 cell generation with as much regularity as to size and form as do 

 the chromosomes, but those who believe in the individuality and 

 continuity of the chromosomes attribute to the latter structures a 

 causal significance not now ascribed to any other organ of the 

 cell. 



