^ Millime-ters ^ 



Figure 214. — Heart of the oyster C. virginica viewed 

 from the ventro-anterior side. Part of the heart's wall 

 was removed to show the auriculo-ventricular septum 

 and the musculature of the heart. Upper part — ventri- 

 cle and root of the aorta; lower part — two auricles and 

 common efferent veins. Drawn from an unpreserved 

 preparation. 



nections between the nerve cells scattered in the 

 heart muscle and nerve fibers entering the heart 

 have not been demonstrated. 



A summary of the results of many investigations 

 of the innervation of the bivalve heart was 

 given by Esser (1934), who denied the e.xistence 

 of the cardial ganglia in tlie heart of Anodonta 

 cyijnea and stated that tlie so-called nerve cells of 

 the nioUusk's myocardium have none of the typical 

 features of the nerve cells. He thought that 

 these cells were identical with certain amoebocytes 

 of the blood of Anodonta. It is true that the 



amoebocytes found in the heart muscle of C 

 virginica have a certain similarity to the cells 

 depicted by Esser. In structure and in general 

 outline they differ, liowever, from the nerve cells 

 and can be recognized in the preparations stained 

 with methylene blue. Under high magnification 

 the ganglia cells in the myocardium of C. virginica 

 appear to be oval-shaped and bipolar (fig. 221) 

 rather than unipolar as described by Suzuki 

 (1934a) for 0. circumpicta. Their cytoplasm con- 

 tains granules deeply stained with methylene 

 blue. Round granules of larger size distributed 

 along tlie axis of the nerve are visible in vitally 

 stained preparations (fig. 220). Similar structures 

 are shown by Suzuki in his figure 4 (1934b) of the 

 preparation of the heart muscle of the Japanese 

 oyster (C. gigaii and 0. circumpicta). The nature 

 of the granules is not known. 



PHYSIOLOGY OF THE HEART 



Contributions to the study of the physiology of 

 the heart of bivalves have been made by Carlson 

 in a series of papers published during the years 

 1903-09 (Carlson, 1903, 1905a, 1905b, 1905c, 

 1905d, 1906a, 1906b, 1906c, 1906d, 1907, 1909); 

 by Ten Cate (1923a, 1923b, 1923c, 1929); Jullien 

 (1935a, 1935b, 1935c, 1935d, 1936a, 1936b, 1936c); 

 Jullien and Morin (1930, 1931a, 1931b); JuUien 

 and Vincent (1938); Jullien, Vincent, Bouchet, 

 and Vuillet (1938) ; JulHen, Vincent, Vuillet, and 

 Bouchet (1939); Takatsuki (1927, 1929, 1933, 

 1934a, 1934b) ; Oka (1932) ; Suzuki (1934a, 1934b) ; 

 Prosser (1940, 1942); and many others. The 

 literature up to 1933 is adequately reviewed by 

 Dubuisson (1933), and more recent investigations 

 are sunmiarized by Krijgsman and Divaris (1955). 

 The studies cited above were made primarily on 

 the fresh-water mussel Anodonta, on Mytihts, 

 Pecten, and Mya. A relatively small number of 

 observations were made on oyster heart. 



AUTOMATISM OF HEART BEAT 



Most of tlie experimental work on bivalve 

 hearts has been done with excised preparations 

 of the organ kept in a perfusion chamber supplied 

 with the van't Hoff or Ringer solutions or with 

 natural sea water. Few observations were made 

 on the heart in situ. 



An automatic rhythmical beating of the excised 

 oyster heart continues for a long time if the heart 

 is kept in an isotonic solution, preferably in sea 

 water, at normal pH of about 8.0 or in the peri- 

 cardial fluid, and the heart muscle is slightly 



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FISH AND WILDLIFE SERVICE 



