328 ELEMENTARY BTOLOCxY. [CHAP. 



backwardly and forwardly. Wash carefully, and remove a 

 good portion of the outer wall of the external lamina; there 

 will be seen 



a. the afferent branchial vessels^ a series of short 

 parallel trunks, conveying the blood from the 

 above-named sinus to the gills. 



Examine the afferent branchial sinus and note that 

 the injection has passed from it into the ventro- 

 external portion of the excretory organ, having 

 filled the efferent renal vessels. 



b. Open up the pericardium, and remove the auricle, 

 thereupon exposed. Make a small hole in the 

 middle of the vena cava (Sect. F. 2) and inject both 

 backwardly and forwardly, exercising a gentle 

 pressure. Wash carefully, and note that the ex- 

 cretory organ is now completely injected, the 

 colouring matter having passed from the vena cava 

 into the affere?ii renal vessels. 



c. Remove the anterior half of the gill-laminae, and 

 dissect to the level of the vena cava. Follow this 

 into the body; it emerges immediately behind the 

 rectum, and is seen to be formed by the confluence 

 of a number of venous channels — some of the more 

 important of which accompany the intestinal coils. 

 Follow it backwards; it can be traced to the under 

 surface of the posterior adductor muscle. 



The vena cava can be dissected from above, as 

 directed in Sect. F, with comparative ease, in an 

 uninjected specimen; its lumen will admit of the 

 passage of a seeker. 



H. The pallial lobe. 



a. Tease up a portion of the substance of the pallial 



