PROTOZOA AND SPONGES. 381 



whence it was about to be collected again. Hence it is 

 probably the first obscure rudiment of a circulation ; the 

 fluids impregnated with the products of digestion being 

 thus collected and then diffused throughout the soft and 

 yielding tissues. 



The smaller bladder-like spaces that you see in con- 

 siderable numbers in the substance of the animal, are 

 collections of fluid contained in excavations of that sub- 

 stance, which are called vacuoles, differing from vesicles, 

 inasmuch as they seem to have no proper wall or inclosing 

 membrane, but to be merely casual separations of the 

 common substance, such as would be made by drops of 

 water in oil. These vacuoles appear to be connected with 

 the digestive function ; for very many of them are not 

 clear, but are occupied with granules more or less opaque, 

 and of exceedingly various dimensions. That these col- 

 lections of granules are food you will see by the following 

 experiment. 



I mingle a little carmine with the water, just enough to 

 impart a visible tinge to it, and close the live-box again. 

 Already you perceive that some of the tiny globules are 

 become turbid and red, and that their opacity and colour 

 are deepening perceptibly. We see by this that the par- 

 ticles of carmine have been taken into the jelly-like sar- 

 code, and are accumulating in little pellets surrounded by 

 fluids, in these casual hollows of its substance. The 

 process is rendered still more obvious when, as is often 

 the case, some Diatomacean,* with a hard siliceous shell, 

 becomes the food of the Amceba. The apparently helpless 

 jelly spread itself over the organism, so as soon to en- 

 velop it ; the flesh, which, having no skin, can unite with 

 itself whenever the parts come into contact, closes over the 



* The Diatomacece, a term formed from the Greek 81A (dia), through, 

 and TefiveiK (temnein), to cat, are so called from the ease with which 

 their masses may be broken or cut through; whence their popular 

 name of brittle-worts. They are usually considered to belong to the 

 vegetable kingdom. 



