XI 



PHYLUM ARTHROPODA 



641 



mesenteron are five pairs of narrow tubes (Figs. 546 and 547, 

 hep. du.) leading into the substance of a large glandular body, 

 usually termed the liver (hep.), though its hepatic functions are 

 doubtful. Into the long narrow intestine, in the last segment of 



the pre-abdomen, open one or two pairs of delicate tubes the 



Malpigkian tubes (mal.) -which act as the organs of renal excretion. 



Circulatory organs. An elongated tubular heart (Fig. 546, 



hrt.) lies in the pre-abdomen enclosed in a pericardial sinus ; it is 



