



Microns 



30 



Figure 239. — The hyaline blood cells of C. virginica. Very small cells on the left; normal cells on the right. Camera 



lucida drawing of live cells on glass. 



minutes changed its shape foui' times from round 

 to oval and back again. The movement is ex- 

 tremely gradual and consists mainly in bulging of 

 one side of the body. The nucleus is not visible 

 in the live cells and rarely can be seen in stained 

 preparations. The cells are basophilic, staining 

 reddish-purple with Romanowsky's stain. The 

 nucleus stains the same color as the cell. 



The hyaline cells comprise about 40 percent of 

 the total number of blood cells in a sample. This 

 is an average of a number of samples taken from 

 the oysters of Long Island Sound and of Chesa- 

 peake Bay in which blood was drawn from the 

 pericardium, heart, and shell liquor. In the 

 oysters in good, healtliy condition, the proportion 

 of hyaline cells varied from 25 to 64 percent, but 

 the differences were not consistent and did not 

 seem to be affected by the origin of the oysters 

 or by the part of the body from whicli the sample 

 was taken. 



THE GRANULAR CELLS 



The granular cells or the amoebocytes vary 

 greatly in shape, size, and behavior. This un- 

 doubtedly is due to their pronounced ability for 

 amoeboid movement. In live contracted state 

 tliey measure about 6 /x in diameter, but they 

 expand and spread to a much larger size. When 

 fresh blood drawn from the oyster by a pipette 

 is spread on a glass slide, many blood cells form 

 aggregates or clumps. This aggregation or ag- 

 glutination results from the adhesiveness of the 

 cell membranes, which stick on contact with one 

 another (Drew, 1910). In a quiescent stage the 

 cells are usually round and motionless. In about 

 half an hour they begin to expand and separate 

 from the clump. By the end of the first hour 



262 



the amoeboid movement becomes active and the 

 cells disperse themselves and form concentric 

 rings around the clump. 



The cytoplasm and the granules of a moving 

 amoebocyte (fig. 240) flow slowly from the center 

 of the cell out to the edge and push the cell 

 membrane out, forming a pseudopodium. During 

 the formation of very narrow pseudopodia the 

 cytoplasm appears to flow out with the granules 

 arranged in single fUe. Contraction seems to be 

 aflfected all at once over an entire cell area, and the 

 action can be quite sudden. In withdrawing, the 

 cytoplasm sometimes leaves behind it a colorless 

 and empty membrane. Fine hyaline projections 

 called "bristle pseudopodia" (fig. 240, right) may 

 remain extended from the membrane and some 

 can be traced back to it. This seems to confirm 

 the argument of Goodrich (1920) that the bristle 

 type pseudopodium is a fold or thickening in the 

 membrane and not a physiologically active part of 

 tlie cell body. 



Clots of blood cells are often observed in injured 

 blood vessels and the connective tissue surrounding 

 small arteries of the mantle, and can be produced 

 by intercardiac injection of tissue extracts. 

 Infiltration of connective tissue by amoebocytes 

 and intravascular blood clots is usually found in 

 watery green oysters from polluted water (fig. 24 1 ) . 



There is no true coagulation of the oyster blood. 

 The coalescence and clot formation of blood cells 

 outside of the body is the result of the entangle- 

 ment of amoebocytes by the bristlelike pseudopodia 

 or by tlie strands of hyaline ectoplasm (fig. 242). 



The granules of live amoebocytes are usually 

 yellowish-green, with the color much more pro" 

 nounced in green oysters. The staining aflinities 

 of blood cells have been studied by several in- 



FISH AND WILDLIFE SERVICE 



