41 



CIRCULATORY SYSTEM. 



In order to dissect the vascular system of Eledone 

 adequately, it is necessary to inject the vessels. The 

 venous system is best injected from the anterior vena 

 cava, and the arterial system from the base of the efferent 

 blood vessel of one side. As the veins lie more 

 superficially than do the arteries, it is best to follow them 

 out first. If dissecting one specimen only for all the 

 systems, only the main blood vessels, e.g., the anterior, 

 abdominal, genital and efferent arteries, the three venae 

 cavae, and the veins of the arms, can be followed 

 satisfactorily. 



The circulatory system will be described Tinder the 

 following headings: — (1) Blood, (2) Heart, (3) Arterial 

 system, (4) Venous system. 



The course which the blood follows in the body may 

 be briefly summarised as follows : Blood which has been 

 a eialed in the gills returns by means of the two efferent 

 vessels to the auricles, and thence into the ventricle of 

 the heart. From there it passes o\it to the body by the 

 anterior, posterior and genital aortae, and ultimately 

 reaches the arterial capillaries. Thence passing into the 

 veins, it finally enters the lateral venae cavae, which take 

 it back to the gill, thus completing the circulation. 



Blood. 



The blood of Eledone is a clear limpid fluid, of very 

 pale blue colour. For examination it may be easily 

 obtained by opening the efferent artery, at the base of the 

 gill, or the anterior aorta, or again the anterior vena cava. 

 In contact with the oxygen of the air the blue colour soon 

 deepens. The various constituents of the blood are : — 



(1) Small colourless amoeboid and very granular 



