116 



Bellow cells (coelomic epithelium), which have an ex- 

 cretory function. 



The food is forced along the gut by the combined action 

 of the circular and longitudinal muscles of the gut wall, 

 the visible effect being that peculiar wavy contraction 

 known as peristalsis. 



Give an Account of the Excretory System of Lumbricus. 



The principal organs of excretion are the nephridia ; 

 there is a pair in each segment except the first three and 

 the last. Each nephridium is a single tube consisting of 

 a minute ciliated funnel, and a looped main portion which 

 is glandular and solid (the duct passing through the cells) 

 and which ends in a wider, non-glandular, and muscular 

 walled bladder opening to the exterior on the ventral 

 surface of the body. The nephridium traverses the thin 

 wall or septum between two segments ; so that its funnel 

 is in one segment and its looped portion in one behind. 

 The opening of the funnel in the body-cavity is the nephro- 

 stome. 



On the walls of the nephridium there are numerous blood 

 capillaries. The waste from the blood is removed by the 

 glandular cells and passed into the tube ; and the current 

 caused by the cilia of the nephrostome flushes it into 

 the bladder which, at intervals, discharges to the outside. 



The yellow cells also extract waste from the blood ; 

 when laden with it they die, and their remains, in the 

 .fluid of the body-cavity, are engulfed by the wandering 

 ampebocytes. The amoeboctyes go close to the wall of 

 the nephridium, and the effete matter is then removed 

 by the glandular cells. 



The coelomic fluid which is exuded through the dorsal 

 pores (one in each groove behind the tenth segment) helps 

 to keep the skin moist and at the same time destroys 

 bacteria. 



Describe (1) the Blood System, and (2) the Nenous System 



of the Earthworm. 



1, There is a ramifying system of capillaries and a number 

 of larger vessels which have contractile walls and are 



