32 



Our Food Mollusks 



Fig. 5. — Single 

 filament of 

 the gill of 

 the black 

 mussel. The 

 ref erence- 

 letter b 

 marks the 

 point of 

 origin from 

 the side of 

 the body, d 

 is the de- 

 scending 

 and a the 

 ascending 

 limb of the 

 filament, i u 

 an inter- 

 lamellar 

 union, and c 

 one of the 

 patches of 

 cilia uniting 

 contiguous 

 filaments. 



Figure 4. The two rows of tubes represent 

 the outer and inner lamellae. Along- 

 regular horizontal lines are found the inter- 

 filamentar unions (c). They are small, 

 rounded patches, slightly elevated from the 

 sides of the filaments, the cells of which bear 

 long cilia or hairs. These tufts of cilia are 

 placed opposite each other on contiguous 

 filaments, and are intermingled much as one 

 might interlock the bristles of two paint 

 brushes by pushing them together. This 

 intermingling of straight hairs is sometimes 

 disrupted, but they have a slight oscillatory 

 movement, and on being brought in contact, 

 soon work together as before. The inter- 

 lamellar unions (i 11) are bands of tissue 

 reaching across the cavity of the gill, and 

 uniting the two limbs of the same filament. 

 The gills of Pecten (Figure 6) are es- 

 sentially like these, but are more specialized 

 in that, at fairly regular intervals, a filament 

 has become greatly enlarged, in order to 

 support firmly the interlamellar partition 

 which it develops. Another difference is 

 that the filaments between these, instead of 

 lying in a straight line, bend outward in 

 a fold. Such an arrangement allows of a 

 greater number of filaments in a gill. The 

 interfilamentar unions in the scallop are 

 ciliary, but the cilia, instead of appearing on 

 patches as in the mussel, are borne on spurs 

 that project from the filament into the in- 

 terior cavity of the gill, as shown at c s. 



