S2 ILLINOIS BIOLOGICAL MONOGRAPHS [370 



Scolex armed with four three-pointed hooks, never replaced by a pseudosco- 

 lex. External segmentation completely absent. Longitudinal nerves dorsal 

 to the cirrus-sac and vagina, close to the lateral borders. Testes between the 

 ner\'e strands only, filling up the whole medullar\' parenchyma so far as this 

 is not occupied by other organs; a testis-free middle field is quite as infrequently 

 present as a pronounced dorsal layer of the testes. Coiling of the \'as deferens 

 in its proximal almost medially situated part, that portion passing distad to the 

 cirrus-sac only very slightly coiled. Vitelline follicles form a continuous mantle 

 between the subcuticula and the longitudinal musculature, which is broken only 

 at the places where the genital ducts open. 0\'ary, approaching the lateral bor- 

 der bearing the genital openings, lies on the ventral transverse musculature, 

 yet individual ovarian tubules extend partly thruout the whole medulla. Shell- 

 gland just as infrequently median as the ovary h'ing behind it, also usually 

 approaching the dorsal surface somewhat. First portion of the uterus only 

 a weakly coiled canal (uterine duct) which passes thru the proglottis transverse- 

 ly and leads into a large single cavity (uterus-sac) which lies not exceptionally 

 ahead of, but yet partly near the ovar}-, and usually not median but away from 

 the margin bearing the genital openings. The latter also applies naturally to 

 the uterus-openings which breaks thru later. Eggs thick-shelled, operculate, 



T\-pe species: T. «odi</o5a (Pallas 1781) Rudolphi 1793. 



As indicated in the above s\Tionymy the name Triaenophorus has absolute 

 page priority altho Stiles and Hassall (1902:22) have contended that Rudolphi 

 should not have changed the name of the genus in 1819 from Tricuspidaria 

 to Triaenaphorus again, after having used it in connection with the specific 

 description in 1810. The change has become so universally established in 

 the literature that it does not seem justifiable to revert to the name 

 Tricuspidaria which is known to only a comparatively small group of zoologists. 



TRIAENOPHORUS sp. lar\-. 

 [Figs. 12-18] 



Since all of the material at hand was larval, not even the earliest traces of 

 the reproductive rudiments showing in toto preparations of the largest speci- 

 mens, it was, of course, impossible to determine the species with certainty. 



Two types of scolices are present, however, and these agree with the de- 

 scriptions of the organ given by various authors for T. nodidosns (Pallas) and 

 by Olsson (1893:20) and Fuhrmann (1910:88) in parricxilar, for T. rohustus 

 Olsson. It will be seen also in the table below that these two forms are foxmd 

 respectively encysted in the liver, on the visceral organs, or in the wall of the 

 stomach, and encysted in the muscles or free in the intestine of the hosts — 

 in the latter case so firmly attached to the wall as to be deeply imbedded, the 

 mucosa forming a protruding collar around the worm — the only exception 

 being those from the intestines of Esox masquinongy and Stizostedion vitrenm 

 (vide infra). Olsson pointed out that these two species can be readily differ- 

 entiated from each other on account of the situations in which they undergo 

 their development. Whereas the larvae of T. noduiosus are foimd generally 



