338 Osborn . — Spongospora subterranea , ( Wallrot/i ) Johnson. 
tion of these groups as one in which a plasmodium does not form must be 
suitably modified. 
It is hardly safe to express any definite opinion on the significance 
of the dissolution of the nuclei and on the occurrence of chromidia, in view 
of the small amount of evidence at present in our possession. It may well 
be that the nuclei rid themselves of a portion of their trophochromatin 
before entering upon a reproductive phase. However, in the present state 
of our knowledge, such a deduction, involving, as it does, the ‘ binuclearity 
hypothesis’, is unjustifiable as anything more than the merest speculation 
until further facts give the theory a firmer basis. As far as the present 
observations on Spongospora go, this loss of chromatin at the time of the 
formation of the reproductive nuclei is the only one to be observed. No 
constant stream of chromatin leaving the karyosome has been seen as 
described for Sorosphaera. 
The karyogamy observed in Spongospora shows a striking similarity to 
that described by Fraulein Kranzlin in Arcyria and Trichia ; the comparison 
with Ceratiomyxa is less easy. The nuclear fusion cannot be confused with 
a direct division, since, apart from the direct evidence as to its nature, it 
has none of the features of the very definite amitosis that occurs in the 
vegetative amoebae. 
The observations on the peculiar method of karyogamy described for 
Plasmodiophora have not been confirmed by more recent workers, while 
as yet no fusion of nuclei has been observed in the life-history of Soro- 
sphaera 1. It is not impossible that a karyogamy has been overlooked in 
these two organisms, and that further work on them will complete this gap 
in the knowledge of their life-histories. 
It is unfortunate that a more definite account cannot be given of the 
prophases of the two karyokineses preceding spore formation in Spongo- 
spora ; since, except for the enlargement of the nuclei and a contraction of 
the chromatin contents, no further details are known. Maire and Tison figure 
a synapsis in Sorosphaera Veronicae , and they are further of the opinion 
that the two mitoses are those of a reduction, Fraulein Kranzlin has described 
synapsis and diakinesis in the Mycetozoa , so has Jahn in Ceratiomyxa. 
Personally I incline to the view that there is a synapsis in Spongospora , 
and that the two following mitoses are the heterotype and homotype of 
a reduction division. However, in default of further evidence, this must be 
stated as an opinion rather than as a fact, but as an opinion that receives 
considerable support by comparison with the occurrences in Sorosphaera 
and Trichia and Arcyria. 
Accepting, then, the validity of this assumption, it is seen that the life- 
history of Spongospora resembles in the main a Mycetozoon as regards its 
nuclear constitution. The nuclei throughout the whole vegetative period 
are of the haploid form [x generation) ; the diploid state (2 x) being only 
