n8 Descriptive Zoology. 



The Sense Organs. The sense of touch is preeminent. 

 This sense is best developed in the palps, along the margin 

 of the mantle, especially that part of it which forms the 

 borders of the siphons, and in the foot. There is no 

 sense of sight, but the tentacles around the siphons seem 

 somewhat sensitive to light. On a nerve near the pedal 

 ganglion is the so-called "ear sac," of doubtful use. At 

 the base of the gills is an organ sometimes called the 

 "smelling patch," which, perhaps, has the office of testing 

 the quality of the water. The sense of taste is doubtful, 

 though it is probable that there is some discrimination as 

 to what should be taken as food. The clam is sensitive 

 to vibrations communicated either through the soil or the 

 water. 



The Reproductive Organs. These are diffuse glands 

 enveloping the coils of the intestine in the abdomen. The 

 glands in the two sexes (ovaries and spermaries) are so 

 similar that it usually requires microscopic examination to 

 distinguish them. The ducts, both in the male and female, 

 open on the side of the body near the opening of the duct 

 from the kidneys. The eggs, when mature, pass out of 

 the duct and lodge in the gills (more often the outer gills) 

 of the female. They are fertilized by the sperms, which 

 have been set free in the water and are drawn in by the 

 same current that brings the food particles. The males 

 and females may sometimes be distinguished by the greater 

 convexity of the shell in the female, the valves being more 

 bulging to accommodate the accumulation of eggs and 

 young clams in the outer gill. 



Development of the Clam. The young usually develop 

 during the fall and winter. When liberated, the young 

 clams are called Glochidia. They are of different shape 

 from the adult, being ovate, with the hinge at the wider 



