SEA MUSSEL MYTILUS EDULIS. 



145 



characterized by the presence of numerous large granules which in the fresh tissue are 

 yellowish or brown in color. The particular hue of the granules seems to depend upon 

 the food of the animal according to List (1902). If the mussel is starved the liver 

 granules become lighter in color, if fed with algae they become green, and if given india 

 ink or carmine they become black or red, respectively. 



The granules contain albumin particles, fat droplets, and glycogen. 



PHYSIOLOGY. 



Erman (1833) believed that the function of the palps was to sweep into the mouth 

 particles of floating food carried forward in the currents set up by the action of the 

 ciliated gills. It was also considered that they might have a respiratory function. 



Thiele (1886) thought that the chief function of the palps was to transfer food col- 

 lected by the gills to the mouth. He pointed out that their structure and position clearly 

 indicated this. The outer pair extend from the upper lip of the mouth to the outer pair 



FlG. 129. — Cross section of a primary liver canal to the stomach. Fixed in Flemming fluid and stained with Delafield hema- 

 toxylin. X 57S. 



Fig. 13a — Cross section of a secondary liver canal. Preparation same as fig. 129. X 57s. 



of gills, while the inner pair reach from the lower lip to the inner pair of gills where they 

 can pick up the food particles collected by these organs. The rich innervation of the palps 

 suggests that they may possibly function as taste organs. List (1902) questions this 

 latter theory on the ground that observations show it to be only slightly probable, as all 

 foreign bodies which have been transported to the palps are taken into the mouth if they 

 do not exceed a certain size. The experiments of Lotsy (1893), however, indicate that 

 certain shellfish have the power of discrimination in the selection of food, for when 

 clouds of diatoms from a culture were introduced near the ventral opening of the syphon 

 of a clam they were immediately ingested, but when hashes of fish or shrimp were given 

 they were refused or if ingested were forcibly ejected an instant later. Oysters, in a 

 similar manner, exhibited the power of discrimination between different kinds of food 

 which were given to them. How the mollusks were able to distinguish between the differ- 

 ent kinds of food Lotsy does not attempt to explain. Anatomically, however, it seems 

 likely that this center of discrimination is located in the palps. 



