A Simple Device for measuring the Volume of an Aquatic Animal

Abstract

DIFFERENT methods of determining the volume of small animals have been described by Lowndes, Holter, Kuenen and Smallman¹. None of these is convenient and simple for rapid measurements. I have found the volumometer sketched here very useful. It consists of a long capillary tube T with a small cylinder C closed with a stopper S to ensure a vacuum seal. The capillary and the cylinder are filled with water and the cylinder is then closed with the stopper. By using the screw-head H at the bottom, mercury is forced from below and the water is raised up the capillary within the stopper to the mark M. Using a hand lens, the base of the water column in the capillary T is read to a fraction of a millimetre. Water is lowered well below the stopper. The creature whose volume has to be measured is dried with filter paper and dropped into the cylinder. When the stopper is replaced, the water is raised to the mark once more and the position of the base read. If the creature cannot be safely wiped with filter paper, the water in the cylinder is lowered until a short column of air enters the capillary and the animal is pipetted along with a minimum of water into the cylinder. The water around the creature is drained into the capillary, and a spill of filter paper is used to remove the last traces of water. The stopper is replaced and the column of water thus drained from the creature is measured. Next, the water is raised to the mark and its position read once more. The last reading minus the column of water drained from the animal will give the volume of the animal.