Dixon — First Mitosis of Spore-mother-cells of Lilmm. 5 



were brought together from different regions of the dolichnematous 

 thread. 



(5.) Immediately after the nucleus enters on the strepsinematous 

 stage, the coils of its thread appear less intricate ; if the twisted 

 portions were formed by the longitudinal fission of the dolichnematous 

 thread no such diminution of complexity, but rather the reverse, 

 should appear, while the approximation of distant parts of the thread 

 and their coiling round one another would leave the nuclear cavity 

 less encumbered, and bring about the less intricate appearance. A. 

 comparison of fig. 1 with fig. 2, and also of Schalfner's fig. 10 with 

 fig. 8,^ will exemplify this point. 



(6.) [Finally, intermediate stages between the dolichonema and the 

 strepsinema stages often present themselves which appear to connect 

 these two stages without the intervention of any longitudinal fission 

 (fig. 10). In these stages the approximating portions are still more 

 distant from one another than they are in the strepsinema condition, 

 but still an indication of the looping and twisting of the thread can be 

 made out. 



These considerations still incline me to the belief that the strep- 

 sinema condition is brought about by the twisting of the originally 

 simple thread upon itself. But I believe it is quite possible, and even 

 probable, that each of the two twisted portions undergoes a longitu- 

 dinal fission while still in the strepsinema stage or immediately after 

 the difEerentation of the chromosomes. This fission has been figured 

 by Schaffner,^ Guignard^ and Gregoire.^ The last two authors, how- 

 ever, regard this as the second longitudinal fission, while the first 

 agrees with the point of view urged by me, regarding it as the only 

 longitudinal fission. Schaffner, however, curiously enough also 

 believes that the strepsinema condition arises by this fission. I have 

 myself frequently observed appearances, both while the thread was 

 intact and immediately after it had broken into separate chromosomes, 

 which might be interpreted in this manner. But considering that 

 such appearances might be produced by interference phenomena* 

 round the sides of such minute bodies as the chromomeres, one cannot 

 be positive that they have an objective reality in the longitudinal 

 cleavage of the chromomeres. 



^ Zoc. cit. ~ Loc. cit., fig lib. 



^ Guignard ; Le dev. du pollen dans le Najas major. Arch d'anat micr. 20 

 mars. 1899. ^ Loc. cit., fig. 10. 



*Tlie Microscope. Naegeli and Schwendener. Eng. Trans, p. 238. 



