374 Wisconsin Academy of Sciences, Arts, and Letters. 
mature spore appears to come about through a reverse in the proc¬ 
ess of nuclear division brought about by the expansion of the 
nuclear vacuoles. At about the time the spores are formed there 
seems to be a change from expansion of their protoplasm to a con¬ 
traction, due to a loss of water. At the same time the nuclear 
vacuoles shrink in size and the chromatin bodies of each nuclear 
structure reassemble to form a single chromatin mass. They re¬ 
main in this condition until after spore germination, at which 
time they resume division. 
Although it is impossible to state definitely which structures de¬ 
scribed by other workers correspond to structures that I have de¬ 
scribed, it is quite plain that most workers have found many of the 
same structures in different mucors. 
The non-staining ‘‘cytoplasm’’ of Dangeard and Leger (1894) 
is undoubtedly the vacuole that I have described as associated with 
most nuclei. Leger (1895 a) believes that in aged hyphae the 
nuclei becomes reduced to nucleoli and persist after the rest of the 
protoplasm disappears. I find a similar condition in many of the 
aged hyphae, considering that the nucleole described by Leger is 
identical with what I have described as a nuclear structure, con¬ 
sisting of one or more nuclei associated with a vacuole which has 
become filled with a reserve protoplasm. 
Istvanffi (1895) describes the nuclei in the growing tips of the 
mycelium as small homogeneous bodies. This conception of a 
nucleus is what I hold for the nucleus throughout the life history 
of the two forms I have studied. 
I find no formations in the two forms I have studied that corre¬ 
spond to the dividing nuclei in the protospores of Pilobolus as fig¬ 
ured by Harper (1899), in which he interprets fibrous strands be¬ 
tween two nuclei as the remains of spindle fibers. 
Swingle (1903) has described the nuclei of Khizopus and Phy- 
comyces as having two or three nucleoli. These are undoubtedly 
what I have described as the daughter chromatin bodies of a single 
nucleus. His description of disintegrating nuclei in the columella 
of Rhizopus and aged mycelium of Phycomyces corresponds very 
closely to my description of the nuclear structures with reserve 
material in aged mycelium, which later may become active upon 
resumption of growth on the part of such mycelium. Other work¬ 
ers have frequently referred to similar nuclear disintegration. It 
seems probable that the disintegrating nuclei in zygospores men- 
