8 NEW YORK STATE MUSEUM 



cally small, it is supplied with no special organs such as teeth or 

 rasping structures. 



I would call particular attention to the relation in position 

 between these palps and the anterior edges of the gills; for I wish 

 presently to describe the manner in which food is transferred from 

 gills to palps, and by these into the mouth. 



When the gills are removed, there is exposed the main mass of 

 the body [vm, fig. 2] which is made up chiefly of a large colored 

 gland, the function of which is the secretion of the digestive fluid, 

 and the greatly developed sexual glands. This body in anatom- 

 ical descriptions, is called the visceral mass, to distinguish it 

 from the muscular organ which is developed on its under or 

 ventral surface the so called foot, f. The last named organ 

 is represented in the figure as being contracted within the 

 mantle chamber. It is capable of great distension and, in a 

 large clam, may be projected for a distance of two or three 

 inches from the edges of the shell. Though a fleshy structure, 

 it is, when protruded, quite tough and firm, being made rigid by a 

 large quantity of blood which is pumped into it by the heart, in 

 order to cause its distension. The foot is an organ of locomotion, 

 and is also used in burrowing. It is possible for Venus to creep 

 about by means of its thrusting and wormlike movements; but I 

 believe that the animal uses it in this way much less than is 

 generally supposed, and this is a point of much interest to the 

 clam culturist. 



In order to understand the mechanism by means of which food 

 is collected, it is necessary to describe in more detail the structure 

 of gills and palps. The gills are the most complicated organs 

 in the bodies of lamellibranchs, and must be described here as 

 briefly and as simply as possible, without mentioning their won- 

 derful histological structure. Outer and inner gills are practically 

 the same. Suppose that one of these is carefully removed from 

 its line of attachment to the body, and studied by means of the 

 microscope from the surface and in section: such an examina- 

 tion shows the gill to be not a solid flap or fold, but an 

 exquisitely minute basketlike structure with an outer and 

 inner wall inclosing a space between. These walls are made 



