CAUSES OF VAEIATION 131 



vacuole does not divide, but remains in one half of 

 the animal, and a new one is developed in the other 

 half. 



Can we account for this by the action of physico- 

 chemical forces? If we suppose that water con- 

 taining uric and carbonic acids gradually collected 

 in one place until it burst through the protoplasm 

 and escaped, we could not expect that this action 

 would be confined to one place, always in the 

 ectosarc, and that it would be regular in its pulsa- 

 tions. No observer has supposed that this is the 

 cause, and the very name contractile vacuole shews 

 that the contraction is thought to be a movement of 

 the protoplasm. The fact that the vacuole always 

 remains in the same place proves that, even in 

 Amoeba, there must be some special arrangement 

 of the protoplasm surrounding it ; and this arrange- 

 ment could not have been brought about by the 

 action of external agencies. 



But suppose that the vacuole originated by the 

 concentration of water containing excretary matters, 

 and that, when it had increased to a certain size, 

 the protoplasm was so irritated that it contracted 

 and expelled the offensive matter. This would be 

 a truly vital operation. Then, after fission, the 

 formation of a new vacuole, always in the ectosarc, 

 must also be a mental operation. These actions 

 may be unconscious, or reflex, now ; but that could 

 not have been the case when the first performance 

 took place. Both actions must at first have been 

 subconscious, even intelligent ; and the arrangement 

 of the protoplasm, which necessitates the vacuole 



