62 ILLINOIS BIOLOGICAL MONOGRAPHS [62 



The parthenita (Fig. 26) is a relatively small, elongate redia, 1.7 mm. in 

 length and 0.35 mm. in transverse section near the middle. It is attenuately 

 obtruncate, with the posterior end sloping down to a blunt point. The 

 pharynx is muscular but small, 60/x in cross section, and aspinose internally 

 (Fig. 31). The rhabdocoel gut extends posteriad about three-fifths the body 

 length. The posterior end is filled with cells, composed of a central rachis 

 with apex directed posteriad, and an outer cell complex of goblet cells (Fig. 30). 

 The central rachis comprises the germinal epithelium, the proliferating region of 

 which is situated sub terminally. From this epithelial mass the matured 

 parthenogenetic eggs are proliferated forward so that the germ balls come to 

 He in the lumen posterior to the gut. Similarly to those in C. pellucida, only 

 the maturing cercariae come to lie around the gut. 



The excretory system of C. konadensis consists of the circuitous trunk 

 system, opening posteriorly into a non-muscular vesicular bladder. This 

 vesicle measures 16ju to 17/^ in width and 14/x to 15^i along the longitudinal 

 axis of the cercaria. The excretory pore is dorsal, opening from the middle 

 of the bladder (Fig. 29). 



The digestive system is of the usual triclad type, with no distinct pharyn- 

 geal region. 



The genital organs are notocotylid in character, but different in several fea- 

 tures from those of C. pellucida. The ovary (Fig. 28) is skull-cap shaped, with a 

 distinct Laurer's canal. A short oviduct leads into the ootype. The uterus, 

 emerging from the ootype, runs cephalad, ending in a swollen vagina some 

 distance behind the Une joining the paired eye-spots. The vitellaria consist 

 of a double series of five inner and three outer follicular masses. The indi- 

 vidual glands are very diffuse and dendritic. 



The testes are small, lateral, and posterior to the ovary, with the vasa 

 efferentia describing a broad crescent anteriad around the ovary and meeting 

 in a common tube, the vas deferens, which runs forward to the left and parallel 

 to the uterus. The vas deferens ends in a swollen cirrus pouch (Fig. 25). 



The nervous system corresponds to the monostome type described for C. 

 pellucida, except that the dorsal trunk to the median pigment eye-spot is 

 lacking. 



In the tail six paired groups of gland cells, derived from parenchyma, 

 occupy places just lateral to the median canal of the excretory system, each 

 group dove-tailing into the one next proximal. These caudal glands indicate 

 a much closer kinship of this worm to Cercaria urbanensis than to C. pellucida. 



Encystment is brought about by the pouring out of the contents of the 

 cystogenous cells and by subsequent decaudation. 



HOLOSTOMATA 



Cercaria flabelliformis Faust 1917 



Cercaria flabelliformis is the first larval holostomid to be described in 

 detail for North America. Leidy has Usted Tetracotyle typica Diesing from 



