1 66 



BULLETIN OF THE BUREAU OF FISHERIES. 



— BrP 



--CJ 



The free ends of the filaments which form the ascending lamellae are hook-shaped, 

 with their anterior and posterior ends firmly attached to each other. This free edge is 



traversed for its whole length by the efferent bran- 

 chial blood vessel (fig. 148, EB V), which increases 

 in size toward the anterior end of the body. 



The plicate canals or Organes godronnes of Saba- 

 tier(i874) are membranous structures which extend 

 from the mantle to the base of the gills across the 

 tip of the angle formed at the junction of these two 

 organs. They are so arranged as to form a series of 

 parallel lamellae running forward slightly oblique to 

 the line of attachment of the gills (fig. 134, EPIC, 

 andfig. 135,/P/Cp. 153). Externally they appear 

 as smooth triangular plates covered with a fine 

 ciliated epithelium (fig. 118, PIC, opp. p. 138). 



They are composed of two thin membranes of 

 fibrillar connective tissue united to each other by 

 strands of the same kind of tissue, which form a 

 regular spongy reticulum in the cavity. The space 

 between them is a blood channel which connects 

 the veins of the mantle with the blood vessels of 

 the kidney and with the longitudinal vein. 



PHYSIOLOGY. 



Primarily the gills of Mytilus function as food- 

 collecting and filtering organs ; secondarily they serve 

 as organs of respiration. By means of the power- 

 ful cilia which cover the gills, strong currents of 

 water are swept in by way of the inhalent syphon. 

 The strength of the current flowing out of the ex- 

 halent syphon is frequently so strong as to make the 

 water appear to be boiling over a mussel which is 

 lying 2 or 3 inches below the surface. The floating 

 food materials, consisting of diatoms, protozoans, 

 and minute organic particles, are thus swept in by 

 these food currents where they are filtered out and 

 transported to the mouth. The currents of water, 

 in addition to bringing in a constant supply of food, 

 also carry the necessary oxygen for the respiratory 

 exchange which takes place through the gills, pli- 

 cate canals, and the mantle wall. 



The action of the different sets of cilia in per- 

 forming this function has been ably studied by 

 Orton(i9i2). He found that the lateral cilia which 

 lash across the length of the filaments are the chief cause of the inhalent current and 

 that the frontal cilia which lash toward the free edge of the gill collect the food 



151 



Fig. 151. — Lateral view of a portion of a lamella 

 showing three gill filaments. X 130. BrF, bran- 

 chial filaments; CJ, ciliary junction. 



