PARASITIC FLATWORMS 

 126 (125) Four suckers on the scolex of the larva. 



Cystlcercus 



451 



127 



The head of the larva is inverted so that these suckers are in the center „f the mass and mav 

 easily be overlooked. In the narrower sense the term cystlcercus is applied to the lar^'e thin- 

 walled bladder-worm having a cavity of considerable size filled with watery fluid in which the 

 scolex grows from a polar papilla that subsequently hollows out giving in reverse the srolov Af ih.. 

 adult This larva belongs to the terrestrial fauna and occurs only SJnl^lly in aquatc form 

 hke the muskrat which have become a part of the acjuatic fauna secondarily. 



127 (128) Entire larva solid parenchyma tissue, 

 apex at bottom of infolding. 



Scolex invaginuled with 

 Plcroccrcoid. 



Caudal region not differentiated at all or only very poorly indi- 

 cated. In general structure the Bothriocephalid larvae with two 

 sucking grooves are like the true plerocercoids with 4 acetabula 



Larvae prominently of Proteocephalidae, also of Cycloi)hyI!idea 

 from reptiles. One special form known as Gryporhynchus has been 

 identifaed as the larva of Dilepis or some allied genus. 



Fig. 763. Proteocephahis plerocercoid; a, from the body cavity b from 

 cyst suckers drawn within body. Note iar-e end organ, shaded; c\ from 

 intestine; optical sections, X 10. (After La Rue.) 



(127) Spaces in larva between folds of tissue, 

 surrounded by cyst 



Scolex in natural position,, 

 Cxsticcrcoid. 



Usually with caudal appendage in a posterior hollow of the cyst, and on the tail the embrv- 

 onic booklets of the onchosphere. In form and texture the cyst varies greatly. Calcareous 

 bodies abundant, mostly on the invaginated layer between the cyst and the scole.x which corre- 

 sponds to the neck when the larval head is evaginated. 



Very frequent among Cyclophyllidea. Relationship between the cysticcrcoid and the adult 

 may be inferred from careful e.xamination of the scolex and its armature. 



No records exist of the 

 presence in North .Ameri- 

 ca of these forms. I-'or 

 convenience in recogniz- 

 ing them a figure is in- 

 cluded of an abundant 

 European form likely to 

 occur here also in similar 

 aquatic hosts. W hile 

 these cysticercoids are 

 most fretjuently recridid 

 from t\)pepoda. Ostra- 

 coda, and other small 

 aquatic Crustacea, they 

 occur also in l.unibruu- 

 liis and other .'■mall an- 

 nelids, and more rarely in 

 small snails and slugs. 



Fic. 764. Drttanidotantia 

 fiiu idtd. a, IkkIv of Cyili^t's 

 <m;»/«5. containlru- l.tx .1 

 i.i|><."worm (c\ ■ 

 simc Iar\-a wi; 

 lon>: tail, isol • 

 crustaci-an; 

 with cxtrndf 

 nil'iol. (.\ft( : 



