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from one hour to four or Jive : the difference in time depends upon the 

 size of the object and its nature, that is, whether it is soluble or 

 insoluble, — on the size or vigour of the leaf, — and whether it has 

 lately been in action. A living insect excites it more than a dead 

 one, as in struggling it presses against the glands of many of the 

 tentacles. An insect such as a fly, with thin integuments through 

 which animal matter in solution can readily pass into the surround- 

 ing dense secretion, is more efficient in causing prolonged inflection, 

 than a thick coated one like a beetle. The inflection of the 

 tentacles takes place indifferently in light or darkness, and the 

 plant is not subject to any so called sleep-like movements in the 

 night. If the glands on the disc are repeatedly touched (although 

 no object is left on the leaf) the mai'ginal tentacles curve inwards. 

 So again, if various fluids such as saliva, or milk, or salts of 

 ammonia, are placed on the central glands, the same results quickly 

 follow. Not only the tentacles but the blade of the leaf often 

 becomes incurved. Drops of milk, and a solution of nitrate of 

 soda, arc particularly apt to produce this result, and the secretion 

 from the glands of the leaf is increased when particles of carbonate 

 or phosphate of ammonia are placed on the leaf. A bit of meat or 

 an insect brings about the same action, and the secretion becomes 

 acid. The glands also have power of absorption. About the 

 mechanism of these movements, and the natui'e of the motor 

 impulse we know very little. 



The DiatomacesB are very minute organisms, which live 

 commonly in stagnant water, in which the majority can move 

 about freely. When placed under the microscope they are found 

 to consist of symmetrical siliceous valves enclosing organic matter. 

 These valves are closed by a line of suture along which they usually 

 divide when producing new individuals, and these frustules are 

 supposed to be pierced by minute holes. The motion of diatoms is 

 of a peculiar kind, a slow regular advance in a direct line, and 

 they do not shrink from, or avoid, any body which may be in their 

 way. The rate of movement is slow compared with that of 

 some of the infusoria, but as compared with the crawling move- 

 ments of some animals it is exceedingly rapid. No organs capable 

 of producing these movements are apparent. Various suggestions 

 have been offered to explain them, such as (1) the existence of 

 endosmosic and exosmosic currents, (2) the existence of cilia in 

 some part, (3) a snail-like foot protruded from the frustule. It 

 seems, however, from an elaborate memoir by Professor Schultz, 

 that the clear hyaline matter within the frustules flows slowly over 

 the exterior of the valves, moving with the inner protoplasm, the 

 flow of Avhich is more obvious from the presence of granules. 

 Hence the band of protoplasm has the nature of a foot by which 

 the diatom creeps along. The same kind of movement may be 

 seen in the desmids. 



