172 



SCIENCE. 



[N. S. Vol. XI. No. 266. 



freely enter the mantle chamber. When 

 the foot is partially retracted and the sphinc- 

 ter muscle around the anterior opening con- 

 tracts, this channel is entirely obliterated. 

 A strong contraction of both longitudinal 

 and radial pallial muscles, and a further re- 

 traction of the foot, fold the mantle and 

 the elastic cuticle into the mantle chamber. 

 At the same time the contraction of the 

 adductor muscles bring the calcareous mar- 

 gins of the shell nearer together, and the 

 mantle chamber is nearly obliterated. As 

 the anterior opening has been closed, the 

 water contained in the mantle chamber is 

 driven through the small posterior opening. 

 Relaxation of the pallial muscles and pro- 

 trusion of the foot again affords ample op- 

 portunity for water to enter the mantle 

 chamber, and the elastic cuticle expands 

 this chamber to its greatest capacity. 



By means of the jets thus formed animals 

 frequently swim some feet before settling 

 to the bottom. 



Most lamellibranchs possess the power 

 of sending jets of water from the mantle 

 chamber, but they generally depend upon 

 forcibly shutting the shell. Pecten and 

 others swim by means of currents produced 

 in this way, but with most it seems to do 

 little more than free the mantle chamber of 

 dirt. Other forms such as the soft clam, 

 Mya, send very strong jets out of their 

 siphons, and depend upon the contraction 

 of muscles in the mantle as well as on clos- 

 ing the shell, to do it. 



Until something further is known about 

 the life and feeding habits of Solenomya, 

 we can hardly expect to know the full sig- 

 nificance of this mode of expelling water. 

 Very possibly the jets are of value in clean- 

 ing the mantle chamber and burrow, and 

 the animal has made use of them second- 

 arily as a means of locomotion. 



The ciliary mechanism in the branchial chamber 

 of the pelecypoda : J. L. Kellogg. 



The fact is well known that minute par- 

 ticles of matter suspended in water, whether 

 they are to be used as food or not, are, 

 upon coming in contact with the surface of 

 the gills ; driven forward and transferred 

 to the inner surfaces of the palps. By 

 these organs they are passed, in the same 

 manner, to the mouth. 



It is usually assumed that the animal is 

 able to control this automatic process of 

 filling the digestive tract only by closing 

 the shell and thus preventing the ingress 

 of water bearing suspended matter. There 

 exists, however, a complex mechanism, 

 differing in many respects in different spe- 

 cies, by means of which suspended particles 

 may be removed from the body, while water 

 necessary for respiration (especially in ac- 

 tive forms such as Yoldia) still continues 

 to flow into the branchial chamber. 



This mechanism in the common soft clam, 

 Mya, may be described briefly as follows : 



(1) There is to be found a complete 

 ciliation of the inner surfaces of the mantle 

 folds. Cilia drive foreign bodies from all 

 points of these surfaces to vortices (one on 

 either mantle fold), situated at the side of 

 the opening for the foot in the fused mantle 

 edge, anteriorly. The vortices are within 

 reach of the palps, and food here collected 

 may be taken by them. If the accumulated 

 matter is not desired, the mass eventually 

 falls upon a ciliated tract which carries it 

 posteriorly along the ventral median line 

 of the fused mantle edges, to a bay at the 

 base of the branchial or incurrent siphon. 

 From this point it is lost from the body, by 

 the violent contractions of the adductor 

 muscles, resulting in the discharge of the 

 greater part of the water contained in the 

 branchial cavity. 



(2) The general ciliation of the surface 

 of the visceral mass causes a movement of 

 particles to a vortex opposite the base of 

 the branchial siphon. Perhaps if desir- 

 able, this material upon the surface of the 



