THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 79 
formed by the parasite. Thélohan now believes a true membrane to 
be absent, the pseudo-membrane being merely the denser, most external 
layer of the ectoplasm, peculiarly modified (coagulated and contracted) 
under the action of the fixing and hardening reagents. It can then 
take on the aspect of a membrane, the resemblance being sometimes 
even further heightened by its exhibiting very definite striz. 
Sections of a barbel’s intestine showed connective tissue spaces 
each inclosing a my xosporidium with an often very well differentiated 
external zone which presented a very distinct striation. Although at 
first regarding this as a confirmation, Théloban, after a more thorough 
examination, varying the observation methods and studying a great 
number of sections of different myxosporidian species, became con- 
vineced that these pseudo-membranes are artificial productions, the 
result of a rougher action of the reagents on the more exposed external 
ectoplasmic layers, which action accentuates their differentiation and 
exaggerates their characters. In fact this membraniform layer can be 
seen to become continuous, without a line of demarcation, with the 
~ectoplasm proper. 
Further, a similar appearance was sometimes observed in sections of 
the pike’s urinary bladder, where (the myxosporidia being free and 
motile) there can be no question of a cyst membrane. Moreover, the 
distinction is much more apparent in sections after the action of re- 
agents (under which conditions the limit of the 2 layers is clearly indi- 
cated and marked by a continuous, often very pronounced, line) than 
in fresh preparations. 
Thélohan’ says that, as Biitschli remarks, the age of the cyst can 
be inferred from its size, the less adVanced cysts being larger with a 
central zone containing the older spores and an outer one containing 
nuclei and spores in process of formation. The oldest cysts are small, 
contain no nuclei, and spore formation has ceased, only developed spores 
being present. 
SPORE FORMATION 
GENERIC RELATIONS. 
This process exhibits differences which not only serve as ordinal 
characters, but which appear also to stand in some sort of relation to 
generic lines. 
Thus in Glugea we have polysporogenetic pansporoblastic spore for- 
mation within a myxosporidium, the pansporoblast not subpersistent 
as a Sporophorous vesicle. 
In Pleistophora we have polysporogenetic pansporoblastic spore forma- 
tion, no myxosporidium (completely transformed into pansporoblasts?), 
the pansporoblast subpersistent as a sporophorous vesicle. 
1Annal. de Microgr., 1890, 11, p. 204. 
