178 HIDDEN BEAUTIES OF NATURE 



within reach. These are taken to their respective 

 centres. That for building material is collected in a 

 cup, and is gradually moulded into bricks, which by a 

 dexterous and rapid movement of the disc are placed 

 in position on the edge of the wall, and, wonderful to 

 say, remain securely fastened although in water. The 

 time occupied in making a brick varies according to 

 the supply of earthy matter held in suspense in the 

 surrounding medium. Generally three minutes is 

 sufficient. As the creature grows larger his house 

 must increase in size, hence it is cigar-shaped, the 

 narrow end being the base. 



An experiment often tried, is to get these tiny 

 objects to make blue or red bricks. To accomplish 

 this end we place a little indigo in the water. 

 In the course of an hour or two we find that 

 the water is clear and that a few tiers of blue bricks 

 have been added to the structure. We next immerse 

 a tiny supply of carmine, allow an interval of time as 

 before, when the water will again appear clear, and 

 rows of carmine bricks will be found in position. It 

 is thus possible to have a tri- coloured house ; the 

 brown bricks at the base are made of clay found in 

 the pond water, the blue and the red as above 

 described. To see this creature at its best it is 

 necessary to procure those rotifers whose houses are 

 in the early stages of construction, as they are not so 

 sensitive to disturbances as those whose works are 

 more advanced. They work night and day to 

 establish their homes. 



