



Microns 



200 



Figure 215. — Small piece of heart wall of C. virginica showing spongy appearance of muscles. Slightly compressed whole 



mount. Formalin, 5 percent, hematoxylin-eosin. 



stretched by the pull of a light lever to which the 

 aorta end of the ventricle is attached; the opposite 

 end of the ventricle is tied to an immobilized 

 glass rod. Gentle stretching is sufficient to pro- 

 vide the necessary stimulus. Takatsuki (1927) 

 claimed that under these conditions the isolated 

 heart of the Japanese oyster, 0. circumpicta, may 

 remain active for 16 days. Observations in the 

 Woods Hole laboratory show that tiie excised 

 hearts of C. virginica kept in sea water at room 

 temperature continued to beat for 2 to 3 days, 

 but the frequency and the amplitude of beat 

 decreased noticeably after the first 24 hoiu-s. 



The molluscan heart functions as a pressure 

 pump which must develop considerable power 



to propel the blood through the circulatory system. 

 The mechanical force during the systole is pro- 

 duced by the contraction of a trabecular wall 

 made of many anastomosing fibers. This arrange- 

 ment, also present in 0. edulis (Jullien, 1935b), is 

 shown in figures 214 and 215. 



In a number of bivalves {Anodonta, Mytilus, 

 Osfrea) the peristaltic wave in the ventricle 

 starts at the posterior end and progresses forward 

 (DeBoer, 1929; Ten Gate, 1923a, 1923b, 1923c). 

 The contraction of the ventricle compresses the 

 auriculo-ventricular valves (fig. 218) and prevents 

 the reflux of blood into the amides. There is an 

 interval between the contractions of the ventricle 

 and auricles which may be noticed by visual 



CIRCULATORY SYSTEM AND BLOOD 



243 



