Furchungsspindel im befruchteten Ei. 387 
which diverge from each other until they come to lie at opposite poles of 
the nuclei and in the plane of contact between the two. At this stage, 
therefore, there is found at each pole of the two pronuclei one-half of the 
sperm aster and one-half of the egg aster. Each of these couples soon fuses 
into a single aster, and the two asters thus formed lie at opposite poles of 
the first cleavage-spindle, and from them all the asters of the developing 
ovum are derived. 
Im Jahre 1901 hat dann Conklin selbst seine Beschreibung 
modifiziert '). 
Er lässt die „quadrille“ fallen und gibt folgende Beschreibung des 
Befruchtungsvorganges bei Crepidula: „The head and middle piece of the 
spermatozoon enter the egg during the early prophase of the first maturation ; 
the tail does not enter. The head is transformed into the sperm nucleus 
and the middle piece into a large number of deeply straining granules. No 
sperm centrosome or amphiaster is present at any time during the movement 
of the sperm through the egg and no astral radiations appear in connection 
with the sperm until the anaphase of the second maturation. At this time 
radiations appear around the granules from the middle piece; the central 
area of this aster grows rapidly and is filled with coarse granules. This is 
the sperm sphere and it develops pari passu with the egg sphere, which it 
resembles in every particular. Each sphere remains in contact with its 
nucleus and when the germ nuclei have come into contact the egg and sperm 
spheres fuse into a granular mass which partially surrounds the germ nuclei. 
Within these fused spheres the two cleavage centrosomes arise. They are at 
frist quite independent of each other and one is always in contact with each 
of the germ nuclei. After some time a central spindle appears between 
the two centrosomes and the first cleavage is introduced. There is no 
„quadrille“ of the spheres, or asters, as maintained in my first paper (1894) 
on this subject, the appearance of a division of the spheres and their sub- 
sequent fusion by pairs which I formerly described being due to their 
lobulation or even fragmentation in certain cases. On the other hand there 
is good evidence that the cleavage centrosomes are not derived exclusively 
either from a sperm centrosome or from an egg centrosome, but that one 
of these comes from the egg sphere, the other from the sperm sphere.‘“ 
Ich muss gestehen, dass meiner Ansicht nach, weder die 
Figuren, welche die vorläufige Mitteilung Conklins im Ana- 
tomischen Anzeiger (1901), noch diejenigen, welche in genauerer 
Ausführung seine grosse Publikation (1902) illustrieren, für die 
doppelte Herkunft der Centrosomen der ersten Furchungsspindel 
') Centrosome and sphere in the Maturation Fertilization and Cleavage 
of Crepidula. Anatomischer Anzeiger, Bd. XIX, No. 11, 1901 und Conklin 
Karyokinesis and Öytokynesis in the Maturation, Fertilization and Cleavage 
of Crepidula and other Gasteropoda. Journal Acad. nat. sci., 2 Ser., Vol. XI. 
Philadelphia 1902. 
