28 BRITISH FRESHWATER RHIZOPODA. 
reproductive cell being itself and alone the individual 
Protozoan, there is nothing to die, nothing to be cast off 
by the reproductive cell when entering on a new career 
of fission... . Experiment and observation in this 
matter are extremely difficult, but we have no reason 
to suppose that there is any inherent limit to the pro- 
cess of nutrition, growth, and fission, by which con- 
tinuously the Protozoa are propagated. The act of 
conjugation from time to time confers upon the proto- 
plasm of a given line of descent new properties, and 
apparently new vigour. Where it is not followed by a 
breaking-up of the conjugated cells into space, but by 
separation and renewed binary fission (Ciliata), the 
result is described simply as ‘ rejuvenescence.’ ” 
This theory, which Ehrenberg first suggested, seems 
to us to be based upon insufficient data. The available 
evidence is directly opposed to such a supposition as 
the immortality of living matter in any form. The 
protoplasmic cell does “ die and disintegrate.” Oppor- 
tunities for observation, it is true, are rare. One, 
within our own experience, may be worth placing on 
record here. During an examination of pond-water 
an Aimaba entered the field of view, in the condition 
represented in figure 15a. The main body was 
advancing in Ameba fashion by lobular expansions 
anteriorly, but dragging behind a trail of its own 
protoplasmic substance. This was clearly an abnormal 
condition, and in endeavouring to account for it one 
was led to suppose that the organism had somehow 
met with an accident by which its body had been so 
torn as to form a kind of tail with a terminal bulb, 
about midway between which and the main body there 
was a slight thickening. 
Curiosity led us to keep the animal under observa- 
tion for about an hour and a half. During that period 
the terminal bulb became separated and assumed a 
spherical shape: (); afterwards the middle portion 
separated; and at last the main body ceased to show 
any indication of life, and rounded out into a spherical 
