POLYZOA. 303 



of branching tubes, occasionally a rounded mass of spongy appear- 

 ance, and now as a flat lamelliform inarticulated expansion of cells. 

 With some of the marine species the shell of the mussel is covered as 

 with a fine lace. 



It is a remarkable fact that these cells are not always inert. They 

 seem to enjoy some little power of motion. It is well known that 

 the leaves and branches of the sensitive plant (Mimosa) contract 

 and expand under the touch of the finger ; the same phenomenon, 

 according to Mr. Rymer Jones, takes place on touching the cells of 

 certain species of Polyzoa. The moment they are touched they 

 quickly incline themselves ; and the movement is immediately com- 

 municated from one to the other, until all the cells of the community 

 are in motion. 



Returning to the organisation of the little creature which occupies 

 the cell, it is found that the upper and retractile portion, which is of 

 extreme delicacy, terminates anteriorly in a circle of long tentacles, 

 in the centre of which is the mouth. These tentacles are fringed 

 laterally by a series of vibratile cilia. " When the animal displays 

 itself," says Fredol, "this circle of microscopic threads of extreme 

 tenuity first show themselves rising from the summit of the cell ; this 

 is followed by the upper part of its body, which is more or less 

 flexible ; the tentacles follow between the threads, pushing them on 

 one side." 



These tentacles are furnished on the back with appendages like 

 very fine hairs, attached to them nearly at right angles, in addition 

 to the delicate cilia already spoken of, which play a very important 

 part in the arrangements of most microscopic animals. At the 

 moment when the tentacles appear outside the cell, the body of the 

 animalcule, which has the power of expanding or contracting itself, is 

 gradually unrolled. It soon spreads out its pretty little arms, the 

 appendages and cilia beginning their rapid vibrations, until the eye, 

 deceived by the rapidity and regularity of their movements, is 

 dazzled, and the beholder begins to think that he sees rosy drops of 

 dew waving to and fro, twisting and untwisting themselves. The 

 corpuscles which float round the animal are violently agitated, as if 

 they were under the influence of some strong breeze. Unhappy, 

 indeed, is the fate of the unfortunate Infusorium which chance leads 

 at this moment into the fatal circle. 



Darwin, who examined some of these creatures very minutely, 

 tells us that " several genera (Flustra, Eschara, Cellaria, Cresia, and 

 others) agree in having singular movable organs attached to their cells. 

 The organs in the greater number of cases very closely resemble 



