PSEUDOSPORA VOLVOCIS, CIENKOWSKI. 227 
almost all the Pseudospora individuals breaking up within 
twenty-four to forty-eight hours. 
The zygote derived from the fusion of the two gametes 
after a time withdraws the flagella and appears as a round 
transparent little creature, with a just discernible spot which, 
on staining, appears as the nucleus. It now becomes amceboid 
and creeps into a Volvox individual, where it feeds and in- 
creases in size; it destroys the Volvox cell, and is to be seen 
lying in its place surrounded by the brownish-coloured débris 
of the chromatophore. 
The small Pseudospora is usually spherical at this stage, 
and the protoplasm appears slightly granular. The creature 
now either becomes amoeboid again and invades another in- 
dividual, or puts out flagella of the type found in the adult. 
In either case the animal developes directly into the adult, the 
development of the flagella in the former case being merely 
postponed foratime. The young flagellate individual becomes 
very easily amoeboid without losing the flagella. 
The zygotes appear to have some considerable power of 
resisting unfavourable circumstances. Thus on one occasion 
I was able to start a culture from sediment containing them 
in which there had been no Volvox for about three weeks. 
The individuals which first appeared were the small flagellate 
and amoeboid creatures just described ; these gradually deve- 
loped into the normal individuals. 
If immediately after the formation of gametes in a culture 
of Pseudospora motionless Volvox be introduced, the zygote 
developes into the radial form instead of the amceboid or flagel- 
late. Here also, as in the amceboid form, spheres are formed. 
GENERAL CONSIDERATIONS. 
The nucleus of Pseudospora seems to me to indicate a con- 
dition intermediate between the centro-nucleus described by 
Keuten and the metazoa-like nucleus of Actinospherium. It 
is a centro-nucleus in so far as the spindle apparatus is intra- 
nuclear, but the formation of the spindle and chromosomes 
shows a marked advance upon such forms as Huglena. 
