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POPULAR SCIENCE REVIEW. 
into a moist chamber, to prevent evaporation, and left for four 
days. Quite by accident it was examined again, when to the 
surprise and extacy of my friend there was nothing living in 
the trough hut rotifers. The volvoxes were all dead, and lay at 
the bottom of the trough, and the rotifers were voraciously eating 
them. More than that, in two of the dead volvoxes the form of 
a similar rotifer could he distinctly seen imbedded. My atten- 
tion was called to the fact as a “ transformation.” I at once 
saw that this was a case, constantly re-appearing, of the rotifer 
parasitic within the volvox ; and as I had never seen this, or the 
rotifer itself, before, I made a drawing of the whole field of dead 
volvoxes with rotifers devouring them, as seen with 12 diameters, 
and given at fig. 1, PI. CXXXIX., and also made a careful draw- 
ing of the rotifer alone under 80 diameters, which is given in 
fig. 2. I remembered that Ehrenberg had observed at least 
two such rotifers, and on referring, found that my drawing came 
nearest to his Notommata 'parasitica. There are minute differ- 
ences between the form I saw and Ehrenherg’s, and there 
is a discrepancy in size ; but there can be little doubt that 
it is either this form or a variety. I was now induced to 
make another gathering ; and within the cells of four out 
of some thousands of volvoxes I saw the rotifer moving 
with sudden fierce jerks, devouring the young and eventually 
bursting the parent cell and escaping. A drawing of the volvox 
with its parasitic rotifer is seen in fig. 3, where the former is 
slightly out of focus that the latter might he clearly perceived. 
Of course no practical naturalist would have been for a 
moment mistaken here. But a want of knowledge of all the 
facts, and a bias to a certain theory, could easily conclude that 
this was a case of volvoxes being “ transmuted ” into rotifers. 
And the same kind of inference is a possible danger to any ob- 
server with a bias, when the objects are comparatively inacces- 
sible, or their life- histories unknown. But in the instance given, 
would it not he equally just to infer that the Trichina spiralis 
in a man or a pig was “ transmuted” muscle ? or that Toenia 
solium was — say the “ transmuted” villi of the digestive tract ? 
But a case yet more instructive presents itself. In the June 
of 1874, a friend at that time residing at Sandhurst, in Berk- 
shire, sent me a large bottle of water from a pond there, con- 
taining a remarkable monad, with two trailing flagella and a 
swiftly lashing anterior one. The form was quite new to. me, 
and is seen in fig. 4. I did all in my power to keep it alive, 
that I might if possible work out its history when some work 
then claiming all my time should he finished. The water con- 
taining the monads was placed in circumstances that would as. 
far as possible prevent evaporation and admit air. But they 
rapidly diminished in number until the middle of August, and 
