Centimeters 



10 



Figure 237. — Accessory heart of C. virginica. Drawing made from an injected preparation, ad.m. — adductor muscle; 

 cap. — capillaries; cr.p.a. — circumpallial artery; d.br. — dorsal branch; ef.v. — efferent vein; p.br. — posterior branch; 

 p.br.j. — pallio-branchial junction; r.s. — renal sinus; v.br. — ventral branch. 



firms the opinion that the mantle and the wall of 

 the cloaca play significant roles in tlie respiration 

 of oysters. 



The pulsation of the accessory hearts makes it 

 possible for the blood of the pallial sinuses to enter 

 the branchial efferent veins or to be forced into 

 the gills through the lateral afferent veins. The 

 pacemaker system and the nervous control of the 

 accessory hearts have not yet been studied. 



THE BLOOD 



There are two distinct groups of blood corpuscles 

 in bivalve mollusks, the hyaline cells and the 

 gi-anular amoeboid cells. The latter are fre- 

 quently called granulocytes because of the large 

 number of granules in their cytoplasms, or 



amoebocytes and phagocytes because of their 

 ability for amoeboid movements and phagocytosis. 

 Tlie hyaline cells are not entirely devoid of 

 granules but tliey are very sparse. These cells 

 also display amoeboid movement but are much 

 less active than the granular cells. Both types of 

 cells are present in the oyster. 



Samples of blood for e.xaniination may be 

 obtained by puncturing the pericardial wall with 

 a fine glass pipette and drawing tlie desired 

 volume of blood. In the same manner blood may 

 be obtained directly from the ventricle or auricles. 

 vSome blood cells are always present in the shell 

 liquor and on the surfaces of the gills and mantle. 

 A fair sample of cells can be obtained by scraping 

 these tissues with cover slips or by drawing the 

 pipette along them. For examination of live 



260 



FISH AND WILDLIFE SERVICE 



