Antidote for Formalin (Continued)

Abstract

Gastropods provide material for a number of demonstrations. These include: the method of locomotion, the operation of the radula in feeding, and the presence of larval flukes in many of the water-living snails. Pelecypods, too, are useful for demonstration. The following suggestions deal with such pelecypods as the freshwater clams, Unio and Anodonta. 2 7'. Role of the Siphons. A single clam is placed in a dish of water resting on a white background, and allowed to remain undisturbed for several minutes. A pipette is filled with dilute carbon ink. As soon as the siphons are extended, the tip of the pipette is introduced below the surface of the water, and a drop of ink allowed to descend close to the tip of the ventral, or incurrent, siphon. A portion of the ink will be observed to enter the siphon. In fifteen or twenty seconds, the ink is dispelled from the excurrent siphon in a dispersed, fan-shaped spray. 28. Ciliary Action. The mechanism responsible for the water currents in the siphons can be shown by placing a small piece of living gill on a slide, covering it with clam juice, adding a minute amount of carbon ink, and applying a coverglass. Under the microscope, the vigorous beating of the cilia can be observed. It will be further noted that tiny carbon particles have been engulfed by masses of mucus, and that these masses show streaming movements as a result of ciliary action.