5l8 THE INVERTEBRATA 



the aminoacid tyrosin by the agency of an enzyme, tyrosinase. This 

 substance is ejected into the mantle cavity and through the funnel in 

 moments of excitement. 



The next stage in dissection is the opening up of the kidneys by 

 cutting through the thin outside wall. It will at once be seen that the 

 cavity of the organ contains a large amount of spongy excretory tissue, 

 developed round the veins which run straight through the kidney. 

 Just inside the renal papilla is a small rosette which carries the reno- 

 pericardial aperture. This leads into the long narrow renopericardial 



Fig. 380. Vertical section of 6'epia officinalisto showthe relation of the divisions 

 of the coelom. After Grobben. dig.gl. digestive gland ("liver"); fu. 

 funnel ; g.coe. genital coelom ; h. heart ; i.s. ink sac ; k.pap. external opening of 

 kidney; k.t. excretory tissue; nid. nidamental gland; o. ova; pan. "pan- 

 creatic " tissue surrounding the duct of the digestive gland ; pcd. pericardium ; 

 r.p.a. opening into the kidney of the renopericardial canal, r.p.c; sh. shell; 

 St. stomach. 



canal running in the outer wall of the kidney and opening posteriorly 

 into the pericardium, a wide space lying behind the kidneys which is 

 only separated by an incomplete partition from the still more spacious 

 genital coelom occupying the apex of the visceral hump (Fig. 380). 



The median ventricle and the two lateral auricles are spindle- 

 shaped bodies arranged in a line at right angles to the longitudinal 

 axis of the body. Arterial blood is sent to the body from the ventricle 

 by an anterior aorta running dorsal to the oesophagus towards the 

 head and a posterior aorta ; venous blood returns to the heart from the 

 head by a very important vessel, the vena cava, which splits in the 



