86 BULLETIN OF THE BUREAU OF FISHERIES. 



quoted (p. 83). They do not generally migrate or bury themselves, however, but 

 simply become benumbed so that they respond very slowly if at all to such stimuli as 

 the touch of the clammer's hook. Evermann and Clark (1918, pi 256) also observed that 

 mussels are not altogether inactive in midwinter: 



Occasional mussels were observed moving about in midwinter, even in rather deep waters. During 

 the winter of igoo-igoi , an example of Lampsilis luteola, in rather deep water in the vicinity of Winfield 's, 

 was observed to have moved about 18 inches in a few days. Its track could distinctly be seen through 



the clear ice. 



FEEDING HABITS. 



It has been pre\'iously noted that a mussel in normal condition on the bottom 

 keeps a stream of water continually passing in through one of two siphonal openings 

 and out through the other. The food is derived from this current as it passes through 

 the gills. The manner in which the food is collected and taken to the mouth has been 

 well described by Allen (i9i4,p. 128 ff) from studies conducted at the Indiana University 

 Biological Station, Winona Lake, Ind. 



The filaments of the gills are covered with cilia which intercept the particles contained in the water 

 and prevent their passing through the gills with the water. They become entangled in mucus, and 

 through the action of these cilia such particles are wafted toward the mouth in streams. If they are of 

 aharmlessnatureorof food value, they are permitted to enter the alimeutar\' tract. During the incuba- 

 tion of the glochidia, the female gives up a greater or less part of one or both of the gills for marsupial 

 purposes. At this period these parts are of little use for respiration or for the collection of food. 



Cilia similar to those of the gills line the entire branchial chamber, cover all organs which come into 

 contact with the water, and also line the alimentary tract. They are, as is always true of cilia, in con- 

 stant motion during life; they act independently of nervous control and in a single plane. Their con- 

 certed action is in the form of waves — resembling in appearance the passing of a breeze over a field of 

 grain, or the movement of a bank of oars. The direction which these waves or streams take varies in 

 the several organs. But all of the streams taken together are coordinated to accomplish a certain common 

 end. * * * 



The mouth of the Lamellibranch lies nearly as far as possible from the external openings, just 

 behind the anterior adductor muscle. It is thus well protected from the entrance of harmful substances. 

 It is flanked above and below by the thin narrow lips. The upper lip is continuous with tlie outer 

 labial palp on each side, while the lower lip is prolonged into the inner right and left palps. Most of the 

 ciliary currents of the contiguous faces of the palps and of tlie lips are directed forward to the mouth. 

 The outer or noncontiguous faces of both palps and lips as well as the edge of tlie inner face of the lips 

 bear cilia which are directed backward and away from the mouth. Thus particles which find their way 

 between the palps are carried to the mouth. As will soon be seen, ver>- little undesirable matter ever 

 reaches the mouth or palps, but even here Wallengren (1905) has pointed out how selection and rejection 

 may be made. 



* * * The inner surface of the labial palps, except their outer margins, are made up of minute 

 vertical ridges, or furrows. These constitute a quite complex mechanism for the sorting of material. 

 » » * 



Upon the ridges as elsewhere occurs a ciliated epitheliiun. But the ciliary currents are disposed 

 in a unique manner. Upon tlie anterior slope of each ridge the)- are directed backward while those 

 on the posterior slope lead forward. This seeming conflict is not such in fact, because only one set 

 of cilia comes into action at a time. The position of tlie ridges determines which set shall fimction 

 at a given moment. Thus the after slopes are ordinarily brought uppermost, the ciliary currents leading 

 to the moutli are upon the sitfface, while the cilia which lead from the moxith lie somewhat underneath 

 the ridges. So long as no adverse stimuli are received, particles which lie between the palps are tliought 

 to be passed on fonvard from one ridge to another, to the lips and mouth. 



In the event that distasteful matter reaches the palps a reflex erection of the ridges brings upper- 

 most the cilia leading backward and such material is returned from summit to summit to the edge of 

 the palps and discharged into the mantle chamber. * » * 



