6 NEW YORK STATE MUSEUM 



America. But, till very recently, no observations have been 

 made on the growth of any clam. In work for the United States 

 Fish Commission, the results of which have not yet been pub- 

 lished, Mya was reared in many places, the experiments being 

 carried out on a large scale. In many ways the results were 

 astonishing, particularly in regard to the rapidity of growth. 

 Not only was the actual amount of growth observed, but also 

 the conditions under which it was least and most rapid, or 

 altogether impossible. It w r as my desire to continue the same 

 line of work with Venus, as nothing was known concerning its 

 growth or the conditions governing it. Though from lack of 

 time and facilities, these experiments were not extensive, they 

 were most encouraging, and show that this form also increases 

 in size rapidly, even when exposed at low tide. 



Feeding habits of Venus. Growth a matter of food 



Within wide limits, rapidity of growth in clams seems to depend 

 directly on the amount of food. In order to make. clear the con- 

 ditions under which rapid growth is possible, the feeding habits of 

 Venus should be described. 



Before such a description is possible, some anatomical features 

 must be noticed. In a clam bed, the animal lies but a short dis- 

 tance below the surface of the bottom. Though the shell is entirely 

 hidden, the creature reaches up to the water above by means of a 

 fleshy extension of the body, which has the form of a double 

 tube. These tubes are known as the siphons, and may quickly be 

 retracted within the valves of the shell. On a smooth bottom, the 

 ends of the siphons may be seen, when the animal is undisturbed, 

 extending out to the level of the surface. A close inspectipn will 

 show that a steady stream of water is entering one tube [fig. i, 

 in. s] and leaving the other [ex. s]. The margin of the first tube 

 is crowned by short, tactile tentacles. When touched by foreign 

 bodies floating in the water, these sense organs cause a closing 

 of the incurrent siphon, or perhaps a retraction of the entire 

 structure. The microscopic diatoms, which form the food of 

 clams, are so small and so evenly diffused in the currents, that 

 they do not induce these movements. 



