656 THE MICROSCOPE. 



which, he at one time declared to be unicellular animals 

 with a contractile cell-menibrane and contents. The con- 

 tractile substan.ce is characterised by the following attri- 

 butes : it is homogeneous, or finely granular, transparent, 

 of the consistence of albumen, gelatiniform, soft, more 

 refracti re than water, but less so than oil ; insoluble in. 

 water, but gradually decomposed; destroyed by caustic 

 potash ; coagulated and contracted by carbonate of potash, 

 as well as by alcohol and nitric acid ; having the power of 

 forming aqueous cavities, which originate either by the 

 separation of the water contained in it, or by its reception 

 from without ; owing to which the remainder becomes 

 denser and more granular, and lastly, it represents the 

 appearance, in water, of contractile drops, which move like 

 an Amoeba. All these properties had already been observed 

 by Dujardin, in a substance of which the Infusoria and 

 Rhizopoda are principally composed, and which he termed 

 " sarcode ; " the aqueous spaces or hollows he named 

 "vacuoles," regarding them as the most characteristic 

 features of the substance ; these spaces had been errone- 

 ously regarded by Ehrenberg as stomachs. All these 

 properties, however, are possessed by a substance in the 

 plant-cell, which must be regarded as the prime seat of 

 almost all vital activity, but especially of all the motile 

 phenomena in its interior the protoplasm. Not only do 

 its optical, chemical, and physical relations coincide with 

 those of the "sarcode," or contractile substance, but it 

 also possesses the faculty of forming " vacuoles " at all 

 times, and even externally to the cell ; a property, it is 

 true, which has for the most part been hitherto overlooked 

 or misinterpreted. These clear, aqueous spaces, the so- 

 termed vesicular contents, are present in all young 

 cells, and play a considerable part in cell-division, and the 

 sap-currents ; they are in all respects analogous to the 

 vacuoles of the sarcode. 1 



(1) Mr. Huxley has satisfied himself that in all the animal tissues the so- 

 called nucleus (endoplast) is the homologue of the primordial utricle, with 

 nucleus and contents (endoplast) of the plant, the othsr histological elements 

 being invariably modifications of the periplastic substance. Upon this view we 

 find that all the discrepancies which had appeared to exist between the animal 

 and vegetable structure disappear : and it becomes easy to trace the absolute 

 identity of plan in the two, the differences between them being produced merely 

 to) the nature and form of the deposits in, or modifications of, the periplastio 



