190 PHOLADIDJi. 



The important discovery I have just related was made 

 manifest in the simplest manner. On taking up an animal, 

 the siphons of which were largely inflated, I observed that 

 the great mass of water was poured out from the branchial 

 tube, and only a small quantity from the anal one ; on re- 

 placing the animal in water, I was surprised, instead of 

 seeing, as I expected, the water flow up the branchial canal, 

 to observe a powerful column, through the tenuity of the 

 membrane, pass rapidly from the pedal opening, in conse- 

 quence of the relaxation of the mantle around the pedal gape, 

 and fill the branchial vault. This very decisive proof how the 

 water reaches the branchiae induced me to vary the experiment. 

 I placed the animal with the tubes entirely in the water, and 

 the pedal gape out of it ; very little fluid entered the branchial 

 sac, the anal siphon alone imbibed a portion ; and on holding 

 the animal with the siphons downward, scarcely any water 

 issued from the branchial one, and only a little from the anal ; 

 but as soon as I suffered the pedal gape to reach the water, a 

 column was instantly seen to fill it as before. 



I do not mean to say that if the pedal aperture is kept out 

 of the water, some fluid may not be imbibed by the branchial 

 tube ; nature will supply its wants by other channels if de- 

 prived of the accustomed ones. I only insist on the position 

 that the usual canal for the entry of the main body of water 

 for the use of the branchiae in all bivalves is by the pedal 

 and ventral apertures ; that the exit is by both the branchial 

 and pedal fissures of the mantle ; that these actions are ac- 

 complished agreeably to the wants and will of the animal at 

 uncertain intervals by the simple opening and closure of the 

 valves, and that what are called currents by cilia do not exist. 

 I cannot help again observing on this simple solution of a 

 disputed point ; I may call it as simple a one as that of 

 Columbus, when he showed how the egg may be made to stand 

 on its apices ; and yet it is quite decisive of the desired point, 

 how the water is admitted to the branchiae. 



The Secretory Organs^. 

 Under this head, as I propose to offer at a future time some 



