CHAPTER VII 

 THE GILLS 



Page 



Anatomy of the gills --- 121 



Promyal chamber --- - 123 



Gill lamella - 125 



Skeleton.. 126 



The filaments -- 126 



Ostla -- 127 



Ciliary tracts..-. 128 



Terminal groove --- 129 



The muscles of the gills.. 130 



Ciliated cells 132 



Fine structure of the cilia... - 132 



Mechanical properties of the cilium 135 



Metachronal rhythm. ._ 136 



Frequency of beat .- 137 



Effect of temperature 138 



Composition of sea water and ciliary motion.. 139 



Effects of chemicals on ciliary motion 139 



Metallic ions... 139 



Hydrogen ions 140 



Various drugs _. HO 



Inhibition of ciliary movement by antiserum 141 



Effect of pressure on ciliary motion 142 



Ciliary currents of tlie gills 142 



Mechanical work of the laterial cilia.. 143 



Carmine cone method.. 144 



Effect of temperature .._ 145 



Hydrostatic pressure inside the gills 146 



Spontaneous inhibition of ciliary motion 146 



Bibliography 147 



The gills of the oyster and other bivalves per- 

 form several important functions. They play a 

 major part in respiration to which the mantle 

 contributes a minor share. They maintain a 

 steady current, filter the water, and collect food 

 particles which are sorted and separated from 

 detritus and other materials in suspension. Tliey 

 serve for the dispersal of sex cells at the time of 

 spawning, and are used for the incubation of 

 fertilized eggs in tlie larviparous species. The 

 effectiveness of these functions is dependent on 

 coordinated performance of the gill apparatus and 

 on the contractions of the adductor muscle. 



ANATOMY OF THE GILLS 



Within the class of bivahes the structure of 

 the gills varies in an increasingly complex series 

 of modifications. The simplest of these is one 

 pair of plumlike single gills or ctenidia with two 

 rows of flattened filaments on each gill. This 

 primitive type, present in tlie order Protol^rancliia 



(fig. 115, A), is found in Ahicula, Yoldia, Leda, 

 Solenomya, and others. More complex structure 

 (fig. 115, B) occurs in the ark shells (Arcidae), 

 scallops (Pectinidae), oysters (Ostreidae), sea 

 mussels (Mytilidae), and other families of Fili- 

 branchia. This type is characterized by long and 

 slender filaments kept in place by patches of 

 interlocking cilia. In some of the bivalves of 

 this gi'oup, including edible oysters, the gill 

 lamellae are plaited into vertical folds and the 

 reflected plates of the gills are completely united 

 with the mantle and visceral mass. These 

 were formerly designated as a separate order of 

 Pseudolamellibranchia. 



The highest degi-ee of complexity is found in 

 the gills of fresh-water mussels (Unionidae), 

 cockles (Cardiidae), clams (Veneridae), and many 

 other mollusks of the order Eulamellibranchia. 

 In these bivalves the lamellae are joined by bars 

 of connective tissue, the filaments ai-e firmly 

 connected by vascular junctions, and the entire 

 gill has the appearance of a perforated, leaflike 

 organ (fig. 115, C). 



In the order Septibranchia {Poromya, Cux- 

 jiidaria) the gills are degenerate. They are 

 modified into perforated, muscular partitions 

 between the two pallial chambers, and the gill 

 filaments are greatly reduced (fig. 115, D). 



The oyster gills consist of four folds (demi- 

 branchs or plates) of tissue suspended from the 

 visceral mass. Two folds on each side of the 

 body arise from a common ridge or gill axis, 

 which is composed of connective tissue and 

 muscles (fig. 73, g.in.). In a cross section made 

 at right angles to the axis of the gill, each demi- 

 branch is V-shaped, with the two branches of the V 

 forming its ascending and descending lamellae. 

 The descending lamella arises from the gill axis; 

 its opposite number is the ascending lamella. 

 The two outer ascending lamellae, one on each 

 side of the body, are fused with the mantle. 

 The two inner demibranchs are joined together at 



FISHERY bulletin: VOLUME 64, CHAPTER VII 



121 



