636 
T. H. MORGAN 
stable basis. The point has been fully discussed in my account of 
Cerebratulus. Here I need only add that while I agree with Lillie 
that the centrifuge offers an opportunity to settle which alter- 
native hypothesis — center of force versus the mitome theory — 
is correct,^ my own evidence points to the latter as the more prob- 
able interpretation. 
There is, in fact, no need to have recourse to the centrifuge to 
show the relation of the spindle fibres to granules. When the 
germinal vesicle breaks down, the fibres that appear in its area 
show granules arranged in irregularly bead-like rows.^ Through 
the courtesy of Professor Wilson I have examined preparations 
of the egg of Thalassema, where the formation of the fibres is 
clearly shown. The fibres that extend out into the cytoplasm 
are largely free from granules, while those that develop within 
the area of the germinal vesical are covered with granules especi- 
ally at their outer ends. Their later disappearance suggests the 
possibility that they may become incorporated within the fibre 
and even form part of its clear material. Such a possibility 
does not however involve the conception of the center of force 
hypothesis.^ 
Comparison with the frog^s egg 
It is not my wish to enter into a full comparison between the 
results here recorded and those which others ^ and I myself have 
obtained with the frog. Only two or three points will be considered. 
The egg of the frog when set free from its inner membrane 
rotates and orients on the machine. But if fixed, the contents 
may rotate as a whole beneath the denser outer ectoplasm. 
Gravity suffices in time to produce this result on eggs that have 
* These contrasts are those that Lillie has drawn. By rejecting the first I do 
not mean to commit myself to the second further than my discussion of the aster- 
formation implies. 
* See the excellent figures of Griffin, B. B., Jour. Morph., 15, 1899. 
^ I am taking for granted in this discussion that the fibres of the aster are not 
artefacts, but I am far from wishing to deny that in the living egg these fibres 
may be little more than denser tracts of hyaloplasm. 
- ^ The recent papers of Gurwitsch and Konopacka and McClendon relate to 
topics other than these here discussed. 
