Korph. F:l 



is the nerve ring which surrounds the esopha;^us, and this is often 

 difficult to see. 



The Excretory aystom 



The excretory system presents a varied picture in the phylum as a 

 whole. It is simplest in the Class Aphasmidia where there is a sin^jle 

 ventral excretory cell, or renette, iijhich opens through an excretory 

 pore on the midventral line in the region of the esophagus by way of a 

 short to long duct. In the Class Phasmidia, there are two lateral 

 excretory canals imbedded in the lateral chords of the hypodermis 

 throughout most of the body length. They are connected anteriorly and 

 ventrally by a transverse canal, thus forming an H or U shape. A duct, 

 variable in length, connects the transverse duct with the excretory 

 pore. The terminal excretory duct is cuticularly lined in the Phas- 

 midia and can be observed in routine microscopic examinations. In the 

 Aphasmidia, the terminal excretory duct is not lined with cuticle (ex- 

 cept in some plectinae), thus making it difficult to see. There may 

 or may not be tvjo special cells (the renette) associated with the 

 transverse duct. 



In a few genera, including Dorylaimus , no excretory system has been 

 fo\md. Considerable excretion through the digestive tract may occur 

 in all nematodes. 



Circulatory and Respiratory Systems 



Circulatory and respiratory systems are not knownj the movement of the 

 fluids of the body cavity apparently serving these purposes. 



