FEEDING HABITS OF FRESHWATER MUSSELS. 135 



THE RATE OF SIPHONING. 



An effort was made to determine the rate at which water is 

 siphoned through the mussel. If this can be done it will con- 

 tribute to several quantitative studies relative to the feeding 

 habits, and that of the effect of temperature and other conditions 

 upon the activity of the cilia. 



But it is very difficult to attach apparatus for making measure- 

 ments to the siphons of the animal. Intimate contact must be 

 made to avoid leakage and a high per cent, of error. Such contact 

 irritates the mussel, so that it does not behave normally. 



In only one mussel did I succeed in obtaining what seemed a 

 normal circulation of water, when under this annoyance. This 

 was done by placing a short piece of soft rubber tubing in the 

 excurrent siphon. Into the end of this was thrust a calibrated 

 glass tube, having a capacity of 2 c.c. between two given marks. 

 The point of a pipette containing neutral coloring matter was 

 thrust into the rubber just outside the siphon. The mussel 

 with this simple apparatus was put into an aquarium near the 

 lake, where the water could be changed frequently and the lake 

 conditions maintained. A touch upon the pipette released a 

 drop of coloring matter into the tube, where it encountered the 

 stream flowing from the excurrent siphon. 



This individual was a L. luteolus weighing 200 grams with the 

 mantle chamber filled. It required five seconds for the pigment 

 to pass between the two marks upon the tube, whenever the 

 incurrent siphon was opened fully. The reading was repeated a 

 number of times at intervals, with the same result. 



While these are but meager results, they give at least an idea 

 of the volume of water siphoned. At the above rate there are 

 siphoned 24 c.c. per minute, 1,440 c.c. per hour, or 34,560 c.c. 

 per day. To filter a liter of water would require 42 minutes. 



DIGESTION. 



Digestion fluctuates more in the case of mussels than does their 

 feeding. That is, the animal continues to feed regardless of 

 appetite; but the degree with which the food so ingested is really 

 made use of seems to depend upon the relation of supply and 

 demand. At times nearlv all the intestinal contents are found 



