A 



B 



D 



Figure 115. — Diagram of the four types of bivalve gills according to A. Lang (1900). A — Protobranchia type {Nucula, 

 Yoldia, Leda, and others); B — Filibranchia type (Pectinidae, Ostrcidae, Mytilidae, and others); C — Eulamellibran- 

 chia type (Unionidae, Cardiidae, Veneridae, and others); D — Septibranchia type (Poromya, Cuspidaria). 



the central axis of the gills under the common 

 afferent vein (fig. 73, c. af. v.). The section 

 across all four demibranchs resembles two W 

 letters joined together at the center. 



Along the entire length of the gill runs the 

 interlamellar space, which in places is divided 

 by the interlamellar partitions or septae into a 

 series of vertical compartments called the water 

 tubes. The septae end close to the junction of the 

 demibranchs and the visceral mass, so that the 

 upper portion of the interlamellar space forms a 



continuous channel along the horizontal axis of 

 each demibranch. This condition is found only 

 at the upper (dorsal) part of the body at the level 

 of the stomach and above it (fig. 116, A). At 

 approximately the level of the heart the entire gill 

 structure has only three points of attachment, in 

 the center at the visceral mass and at each side 

 where the gills fuse with the mantle (fig. 116, B.). 

 The entire chamber system of the gills can be 

 visualized as four passages which at the level of the 

 heart merge into two epibranchial chambers. The 



ep.ch 



add.m 



ep.ch. 



Centimeters 



A 



B 



C 



Figure 116. — Transverse sections of 1-year-old C. virginica (diagram drawn from sectioned and stained preparations). 

 A — Section at the level of the stomach, s.; four epibranchial chambers at the base of the gills, ep.ch., and proniyal 

 chamber, pr.ch., at right. B — Section near the level of the heart, two epibranchial chambers, ep.ch., are separated 

 by the pyloric process, p. C — Section at the level of the adductor muscle below the heart, common epibranchial 

 chamber, ep.br.ch. Bouin, hematoxylin-eosin. 



122 



FISH AND WILDLIFE SERVICE 



