362 Wisconsin Academy of Sciences, Arts, and Letters. 
nucleus of the vegetative mycelium as consisting of a very small 
homogeneous body, and suggests that it is identical with a chromo¬ 
some. Division of a nucleus in the vegetative hyphae consists 
simply in the separation of the chromatin body into two daughter 
nuclei. He finds that in spore formation in the sporange from five 
to twelve of these chromatin bodies are enclosed within each spore. 
He describes no change in the structure of the nucleus during zygo¬ 
spore formation, except that after the fifth day of development the 
nucleus is spongy and contains a single chromatin body. He re¬ 
ports no nuclear divisions or fusion during the formation and 
maturation of the zygospore. 
The nuclei in the zygospore preparing to germinate are sur¬ 
rounded by a membrane but have only one chromatin body and by 
the time the germ tube pushes out, eleven to twelve days after sow¬ 
ing, the nuclei are more or less irregular in outline and provided 
with several chromatin bodies and a nucleole. At this stage they 
are several times larger than the nuclei of the sexual generation. 
In the germ tube and sporange, nuclear divisions occur among the 
large nuclei. Burgeff states that all stages in mitosis are difficult 
to make out. Clear prophases occur in which the nucleole disap¬ 
pears. The chromatin is separated into twenty-four (estimated) 
chromosomes. Twelve chromosomes move to each pole within the 
membrane; no equatorial plate stage is observed. Burgeff char¬ 
acterizes this as a heterotypic division, following which, he states, 
a homotypic division occurs in which distinct chromosomes are 
present. Following the homotypic division successive divisions 
take place, giving rise to a large number of membraneless nuclei. 
These nuclei, with a number of nuclei surrounded by membranes, 
become the nuclei of the spores formed within the germ-sporange. 
He suggests that the nuclei with membranes are either unfused 
nuclei of the gametes or else nuclei that have not passed through 
reduction division. In spore formation only one nucleus enters into 
the formation of a spore. After spore formation, as they mature, 
the nucleus of each spore divides successively so that each mature 
spore contains a number of nuclei. In his summary, however, 
Burgeff states that he has not observed the division of nuclei with 
membranes within the spores of the germ-sporange. 
Burgeff (1920) describes the nuclei of the parasitic mould, 
Chaetocladium, and of its host, Mucor, as being very similar. The 
nucleus of either form consists of a deep-staining body with or 
without a clear zone surrounding it. The clear zone is more fre- 
