IOWA ACADEMY OP SCIENCES. 
3S 
another process takes place, two individuals becoming adher- 
ent, the cell walls in the region of contact being dissolved as 
punctured, and an interchange of the protoplasm taking place. 
After this the individuals separate and the process of fission is 
renewed, and goes on for many generations. Ultimately, how- 
ever, the process of conjugation is again resorted fco. 
In certain of the Vorticellidce the reproductive process is still 
further complicated by the fact that the fission is not simple 
but multiple, one of the halves resulting from simple fission 
again dividing into a number of small ciliated bodies, each of 
which is capable of uniting with a normal vorticella in the pro- 
cess of conj agation. 
In certain Acinetans the multiple fission is internal, the 
parent cell having its contents broken up into a number of 
ciliated bodies, which escape through the ectosarc. 
We thus see that in going from the lower to the higher Pro- 
tozoa we find the reproductive process growing more and more 
complicated. First in the amoeba we find simple fission, then 
in the Paramecium we find simple fission plus conjugation. In 
the vorticella we have simple fission plus multiple fission plus 
conjugation. In the acinetan we find simple fission plus inter- 
nal multiple fission plus conjugation. 
Such, then, are the facts. We now turn to seek an? 
explanation. 
Anabolism is the constructive, conservative, potential energy" 
of the cell. 
Katabolism is expressed in the destructive expenditure of 
this energy in active or kinetic processes. 
The growth of any normal cell has a necessary limit due to> 
a purely physical cause. The mass increases as the cube oit 
the diameter, while the surface increases only as the square. 
The surface performs the function of respiration, but it cannot 
perform this function for an unlimited mass any more than a 
cubic inch of lung can perform respiration for a full grown 
man. 
As a cell increases in size its mass increases more rapidly 
than its surface, until a point is reached beyond which it can 
not grow, because the surface can supply no more oxygen. It 
is worked to its limit, and can not respond to increased demands. 
At this stage there are three possibilities: 
First. — Death, which would end the question. 
Second . — Stationary balance, which is impossible. 
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