AGELENA N^VIA WALCKEN/ER 167 



Excretory system. Two malpighian tubes function as organs 

 of excretion. They are situated in the abdomen, partly imbedded 

 in the adipose tissue, and open into the stercoral pocket of the 

 hindgut. It is probable that the coxal glands, too, have an ex- 

 cretory function. 



Circulatory system. Agelena has an open circulatory 

 system in which the arteries open directly into the body cavity. 

 The heart is a long tube with muscular walls, situated in the mid- 

 dorsal line of the abdomen, directly under the body wall, be- 

 tween the two lobes of the adipose tissue. It is inclosed in a 

 pericardium and provided with three pairs of lateral ostia 

 through which the blood enters. Anteriorly the heart becomes 

 constricted and forms the anterior aorta which runs above the 

 intestine, enters the cephalothorax and divides into two arteries 

 in the region of the pumping stomach. These arteries subdivide 

 and supply the appendages and the organs inclosed in the ceph- 

 alothorax. Posteriorly the heart gives off the posterior aorta 

 which extends almost to the anus. The blood which is colorless 

 and contains amcebocytes, reaches the lungs by way of lacunae, 

 while a portion of it is oxidized through the tracheal tubes. From 

 the lungs the blood returns to the heart by way of two pulmonary 

 sinuses which open into the pericard at the points nearest to 

 the anterior ostia. The blood oxidized through the tracheal 

 tubes returns to the heart through the four posterior ostia. It 

 is probable that the heart does not contain fully oxidized blood. 

 The rhythmic pulsation of the heart drives part of the blood 

 forward and part backward into the posterior aorta. 



Respiratory system. The respiratory system of Agelena 

 consists of a pair of lung-books and of tracheal tubes. The 

 lung-books are modified and infolded appendages of the second 

 abdominal somite. They are situated in front of the genital 

 groove in little pockets of the integument. The opening leading 

 into the pocket is called the stigma or spiracle and is situated at 

 the rear end of the pocket. The lung itself consists of numerous 

 lamellce attached to the anterior end of the lining of the pocket 



