PSEUDOSPORA VOLVOCIS, CIENKOWSKI. 229 
conditions, and of no phylogenetic weight. In classifying the 
Protozoa it is essential to have regard to the whole life 
history. 
SUMMARY. 
1. A Pseudospora individual may adopt three forms—an 
ameeboid, a flagellate, and a radial form. This last, at least, 
appears to be a direct reaction to external conditions. 
2. A single nucleus is present. It is bounded by a mem- 
brane, which contains the karyosome surrounded by a clear 
space ; fine rays pass from the karyosome to the membrane. 
3. The nucleus divides by mitosis. The chromatin forms 
chromosomes, which are apparently rod-shaped. The spindle 
appears to be formed from the achromatic intra-nuclear sub- 
stance. 
4, Pseudospora reproduces by fission. After fourteen to 
twenty-one days gametes are formed. 
5. Gametogenesis. The nucleus of the Pseudospora be- 
comes converted into a sphere, the nuclear substance of which 
appears to be derived from the rays of the original cell nucleus. 
The karyosome is extruded from the sphere. 
6. The sphere segments to form a large number of gametes. 
7. The gametes conjugate in pairs, forming zygotes, which 
develop into the adult Pseudospora. 
EXPLANATION OF PLATE 12, 
Illustrating Miss M. Robertson’s paper, “On Pseudospora 
volvocis.” 
The figures are drawn under Zeiss apochromatic homogeneous immersion 
objective, three-millimetre focus and compensating eye-piece No. 12. 
Fie. 1.—Ameceboid Pseudospora, with short pseudopodia. 2. Nucleus. 
k. Karyosome. c¢. s. Clear space round the karyosome. 7. Rays passing 
from the karyosome to (m.) the Membrane. £ Food particles. 
Fic. 2.—Ameeboid Pseudospora, with fine pseudopodia arranged in bunches, 
Fic. 3.—Flagellate Pseudospora, 
