KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 183 
view states that at first the two halves of the spindle are 
separate, but later on unite at the level of the equatorial 
plate to form a single structure. The remainder of the spindle- 
threads attach themselves to the chromatic loops of the equa- 
torial plate. Since the nuclear membrane remains present 
during the formation of the spindle figure, the spindle-threads 
have to perforate the membrane, which becomes sieve-like. 
Strasburger believes that there is here an explanation of Flem- 
ming’s view that the spindle-threads can appear inside an 
apparently complete nuclear membrane; but within the nuclear 
membrane, besides the chromatic loops, there are some very 
delicate threads which unite the chromatic loops to the nuclear 
membrane. Whence these delicate threads arise, whether 
they originally belong to the nucleus or whether they pene- 
trate from the surrounding protoplasm, what finally becomes 
of them, whether they unite with the chromatic loops or with 
the spindle-threads, Strasburger leaves undecided. He is 
disposed to derive them from the surroundings of the nucleus, 
i.e. from the cytoplasm, and to believe that they unite later 
on with the spindle-threads; in this respect the spindle- 
threads in Ascaris megalocephala (Boveri and E. van 
Beneden) exhibit the same behaviour asin Spirogyra. The 
greater part of the threads later on stretch from both sides of 
the equatorial plate, but only a small number of them are 
directly connected with it, so that only some few threads 
extend from pole to pole. Boveri finds the same thing in the 
testis-cells of Crustacea. i 
On the other hand, Carnoy (47) believes that in all the 
Arthropods studied by him all the threads reach from pole to 
pole ; the same thing obtains also in the testis-cells of Sala- 
mander, at least in all probability, according to Flemming. 
They have the same relation in the higher plants, according 
to Went (205) and Strasburger (191), whereas Berthold 
(‘ Protoplasma-mechanik’) believes that only a portion of 
the threads extend from pole to pole (in plants). 
Strasburger, however, does not regard his view as to the 
formation of the spindle figure as universal ; in discussing the 
