EXCRETORY SYSTEM IN DIGENEA. 343 



Habitat: Urbana, Illinois, 1918. 

 Flame-cell formula: a -\- a" 4 + 2 or 6. 



Monostome larva of spatulate outline, with a length of about 

 0.5 mm. and a width of nearly half that measurement; tail 

 equally long and capable of great distension along its transverse 

 axis and great extension along its longitudinal axis. Body en- 

 tirely covered with minute spines. Trioculate, with dense masses 

 of melanoidin pigment around the lateral eyes, extending caudad 

 along the six posterior nerve trunks; integument of entire body 

 more or less infiltrated with pigment granules. Locomotor 

 pockets at posterior part of body, small, simple. Tail aspinose 

 with six continuous pairs of large vacuolated cells at sides of 

 caudal excretory canal. 



Oral sucker leading into a long narrow esophagus; esophagus 

 branching some little distance behind the median eye to form a 

 typical furculum. 



Excretory bladder ovate, transversely compressed, with a 

 strong sphincter; main circuitous collecting tubule with a main 

 branch on each side; flame cells anterior to main branch four 

 posterior to main branch two. 



Genital organs consisting of median ovary, paired testes in 

 plane slightly behind ovary, uterus and vas deferens leading 

 forward respectively to vagina and cirrus sac; vitellaria of two 

 series of five inner and three outer glands on dorsal side of 

 body. 



Redia with long rhabdoccel gut, strong pharynx lined with 

 transverse chitinous ribbing, and spines anterior and posterior 

 to pharynx. Birthpore inconspicuous. Flame cells two for 

 each side of the body. 



Cystogenous granules many, densely opaque. Decaudation 

 slow; encystment very slow. 



SUMMARY. 



i. Development of the excretory system in the monostome 

 larva Cercaria spatula nov. spec, gives support to the principle 

 of orderly development and conservatism of the system in mono- 

 tome larvse. 



