80 ILLINOIS BIOLOGICAL MONOGRAPHS [368 



wall in a very small and limited area, and not of a preformed membrane as 

 in the Ptychobothriinae. 



Concerning the eggs Linton (p. 433) said: "The ova are nearly spherical, 

 with thin shells. They are about 0.04mm. in the greatest diameter. " Those 

 from material preserved in formalin were foimd by the writer to be sometimes 

 spherical in shape but usually ovoid or ellipsoid, with maximum dimensions 

 in the latter case of 45 by 36/x. Neither in sections nor in preparations of 

 eggs from the uterus sacs of material in formol, alcohol or cleared in oil of 

 wintergreen were opercala to be found, but at the one pole of the egg a small 

 boss about 5m in diameter which is often enlarged to form a distinct projection 

 or appendage. Altho development had not progressed in any of the eggs 

 studied so far that the six hooks of the oncosphere were visible, the writer 

 is of the opinion that even in mature eggs no opercula would be found, since 

 its almost spherical shape and the presence of the button-like thickening at 

 one pole are quite like conditions in the nonoperculate egg of Abothrium rugo- 

 sum, for instance, as described and figured by Schauinsland (1885:527) and 

 further, since in the egg of the operculate type, as in that of D. latum or of 

 T. nodtdosus, described and figured by the same writer, the operculum is present 

 long before the hexacanth embryo has developed. 



As regards the Mfe-history of this species nothing is as yet known. It is 

 noteworthy, however, that very young larvae, such as shown in figures 46 

 and 47, can be easily recognized on account of the peculiar character of the 

 scolex, so that it would not seem difiScult to pick them out of the intermediate 

 host whatever that may be. AU sizes from the youngest (Fig. 46) to the lar- 

 gest were present in the material studied. 



The material of this species consisted of Nos. 4724 and 4783 of the collection 

 of the United States National Museum, Nos. 16.292, 16.421 and 17.11 of the 

 collection of the University of Illinois and No. 154 of the writer's collection, 

 all from the intestine of Polyodon spathula, the paddlefish. 



