1894. CELL-DIVISION. 47 



ception of the "lame intermediaire " as being part of the spindle. On 

 the other hand, it is possible that the two half-spindles are merely the 

 rays of the archoplasmic spheres, and in no way to be compared to 

 the central spindle. These points obviously still require considerably 

 more light to be thrown upon them. 



The lame intermediaire. — This name was given by Van Beneden 

 to the layer of achromatic substance between the split halves of 

 the chromosomes. It consists chiefly of delicate fibrils (Verbin- 

 dungs Fasern) which lengthen out as the chromosomes increase 

 the distance from one another. Brauer has attempted to dis- 

 tinguish between these fibres and those that form the central 

 spindle, on the ground that the latter are actively contractile 

 while the former are merely connecting threads, but whether this 

 is so or not, there can be little doubt that these connecting threads 

 are formed from some portion of the achromatic network of 

 the nucleus, even in those cases where the spindle may have 

 an extra-nuclear origin. In some cases they appear to persist 

 longest of any of the elements of the karyokinetic figure, remaining 

 visible even if the daughter cells have become completely cut off 

 from one another. The chromatic elements of the nuclear figure will 

 be dealt with in a future paper, but there are two points which should 

 here be noticed, viz. : (a) The mechanics of karyokinesis. (b) The 

 fate of the nucleolus. 



(a) Mechanics of karyokinesis. — More, perhaps might be written on 

 this part of the question than on any other, but it would be 

 almost entirely of a speculative nature. Nothing is really known 

 as to how the chromosomes move towards the poles, although 

 it is the opinion of many that the threads of the spindle are 

 contractile, and so pull the chromosomes apart. Exactly the 

 contrary is the view of Strasburger for plants, and Watase for the 

 cells of embryo Cephalopods. The former believes that the threads 

 of the archoplasmic spheres penetrate through the porous nuclear 

 membrane, forming two half-spindles. The movement of the chromo- 

 somes, he considers, are due partly to their own independent activity, 

 and partly to the fact that they are pushed towards the poles by 

 swelling up of the "lame intermediaire" due to the osmosis of nuclear 

 fluid. 



Watase, on the contrary, although he believes with Strasburger 

 that there is no central spindle, but only two half-spindles, considers 

 that the threads are stiff, like bristles, and flatten out the nucleus 

 into an equatorial plate. By this means they gradually push the 

 chromosomes between one another, eventually carrying one set to one 

 pole and one to another, the membrane of the nucleus being preserved 

 during the whole process. This view, which Watase thinks to be of 

 general application, seems somewhat fantastic ; yet, at the same time, 

 it must be allowed that his figures strongly suggest such a process. 

 It has recently been suggested that the centrosome is by no means a 



