THE AMCBBA. 
193 
all these, together with such intermediate conditions as made 
their specific unity indisputable. Like many others of these 
Protozoa, the Amoebae seem to be endowed with remarkable 
tenacity of life. That they can be dried up and yet retain their 
vitality has been proved by the experiments of Ehrenberg, 
Hicks, Balbiani, Samuelson, and Wallich. In some cases the 
Amoebae appear to have survived the drying process and to 
have revived on being wetted again. In others only certain 
reproductive germs were preserved, the actual animals having 
perished. But in both instances we have provision for the 
perpetuation of the species, wherever a little water stands, or 
damp vegetation grows. The dried-up germs can be diffused 
by every wind, and develop into life wherever the needful 
moisture awaits their reception. Hence the universality of 
their occurrence. 
This reference suggests the question of the actual modes of 
reproduction amongst the Amoebae, and here we enter upon 
another perplexing subject. The simplest mode is by fission 
and germination. A creature merely contracts the middle of 
its body until the two ends become separated, and the divorced 
parts sail away to pursue an independent existence for the 
rest of their lives. In these cases each part usually contains a 
nucleus and a contractile vesicle ; but sometimes the one or 
the other of these organs may be wanting in the newly-formed 
segments. Hr. Wallich has noticed that when the general 
fission of the animal was preceded by fission of the nucleus 
and vesicle, the creature was active, and moved briskly away 
as soon as the division was completed ; whereas when either 
of the organs in question was absent, the separated portion so 
deficient remained torpid as if awaiting their reproduction. 
Instead of the creature dividing into two nearly equal 
halves, a single pseudopodium may become detached in a 
similar manner. But this is a slow reproductive process com- 
pared with others to which attention has been drawn, especi- 
ally by Hr. Wallich. He has shown that Amoebse un- 
dergo a process of encystation, arising, as he supposes, from 
a prolonged contact of the ectosarc with the surrounding 
medium, and from a cessation, due to some unknown cause, 
of the mutual conversions of ectosarc and endosarc. What- 
ever may be the explanation of the action, there appears to 
be no doubt that the animal becomes torpid, preparatory to 
the evolution of important changes in its interior. Previous 
to this encystation, however, the creature extrudes from its 
sarcode all foreign particles, except the frustules of Diatoms. 
These Hiatoms, Hr. Wallich believes to be retained as store- 
houses of nutrition during the encysting process. The 
external pseudopodia disappear. The nucleus, contractile 
