370 Wisconsin Academy of Sciences, Arts, and Letters. 
8b, 8c and 8d. Such figures correspond very closely to those of 
nuclei observed in the zygospore during maturation when the 
vacuoles were beginning to receive the reserve substance. 
An insufficient number of stages were fixed to warrant reporting 
on the process of spore formation in the germ sporange. How¬ 
ever, it has been determined that nuclei of the type shown in fig¬ 
ures 8a, 8b, 8c, and 8d pass into the sporangiophore and are found 
there before and after spore formation in the sporange. There 
appear to be no nuclear divisions in the germinating zygospore or 
in the germ sporangiophores either before or after spore formation. 
Rhizopus Nigricans 
A complete study of the nucleus of Bhizopus nigricans has been 
made in the vegetative mycelium, in the sporanges, in the mature 
and germinating spores, in the gametes, and in the zygospores dur¬ 
ing maturation. Since no germination of zygospores has been ob¬ 
tained, it has been impossible to follow the nuclear behavior 
through that process. 
It is very evident that nuclear behavior is, in general, the same 
in Rhizopus as has been described for Phycomyces in the processes 
of nuclear division and in the formation of reserve protoplasm 
stored in the vacuoles associated with the nuclei of the zygospores. 
The nuclear vacuoles do not become quite as large in Rhizopus 
as they do in Phycomyces. Compare figures 9a, 9b, and 9c taken 
from the sporange of Rhizopus with figures 3a and 3b taken from 
the sporange of Phycomyces; both sporanges were at about the 
same stage of development. 
In Rhizopus the obliteration of the vacuole, causing the separa¬ 
tion of the chromatin masses, takes place sooner after the separa¬ 
tion of the daughter nuclei, and, therefore, in the case of Rhizopus 
one finds more frequently the nuclei disassociated from a vacuole. 
Figure 9e illustrates a case in which two sister nuclei evidently 
were at first associated with the same vacuole and later one of them 
formed a second vacuole, which separated the two chromatin 
masses still further. A third small vacuole also has formed be¬ 
tween them. A somewhat similar case is illustrated in figure lib 
in which a nucleus from a young zygospore has divided and one 
of the daughter chromatin masses is forming a vacuole within an¬ 
other vacuole. Figures 10a, 10b, and 10c are dividing nuclei 
taken from a vegetative hypha. 
