NUCLEAR FUSION IN THE ASCUS. 6 1 



maintains (17, p. 108), also, that in the rotations which occur in the 

 telophases the centrosome and sphere and the nucleus present their 

 same sides to each other throughout. 



Of the more prominent workers on the subject of the mechanism 

 of karyokinesis who have obtained positive evidence of a permanent 

 connection of the nuclear content with the centrosome may be men- 

 tioned Rabl, Flemming, Meves, Kostanecki, and Conklin. Those who 

 believe that the contractile fibers each time form a new connection with 

 the chromosome include Van Beneden, Boveri, Hermann, Druner, and 

 many other recent students of nuclear division in animal cells. 



Montgomery (65) and Paulmier (75) hold that the connection of 

 the spindle fibers with the chromosomes persists between the first and 

 second maturation divisions. Boveri (13) also accepts this view and 

 believes that thus the chromosome reduction is effected in the second 

 division, regarding this case as an exception to the general rule. Paul- 

 mier holds that in the first division the spindle fibers arise by a special 

 orientation of the linin of the nucleus. 



Jenkinson (50), who has approached the question with quite differ- 

 ent preconceptions as to cell structures, and whose results are certainly 

 unreliable on many points, finds that in the origin of the cleavage spindle 

 of the axolotl the membrane of the sperm nucleus appears weakened or 

 wanting on the side where the centrosome first appears, and that the 

 centrosome is here so close to the nucleus as to appear as if emerging 

 from it. 



THE NUCLEAR FUSION IN THE ASCUS. 



The evidence from the series of figures showing the nuclei of the 

 ascogenous hyphse in their later stages of development, as given above, 

 indicates that the fusion of the nuclei in the young ascus does not result 

 in doubling the number of chromosomes as they appear in the succeed- 

 ing divisions, and in this respect this nuclear union differs fundament- 

 ally from any sexual fusion of nuclei in the higher plants or animals 

 in connection with which the chromosome number has been yet estab- 

 lished. There is no visible doubling of the number of chromosomes in 

 the ascus, and while we must assume that the combining chromosomes 

 maintain their identity, the centers unite so intimately that at least 

 nothing of a double organization is visible. On the other hand, the 

 fusion of the ascus is followed at once by a synapsis stage and a triple 

 instead of the ordinary double division of the spore mother cell. We 

 have thus an immediate apparent reduction of the number of the chro- 

 mosomes by one-half, the 16 chromatin strands of the fusing nuclei 

 appearing as 8 strands in the spirem stage of the fusion nucleus and 



