192 ILLINOIS BIOLOGICAL MONOGRAPHS [480 



breadth and about 2mm. in thickness. One from Coregonus clupeiformis 

 measured 292 by 1.8mm. and another 185 by 2mm., while those from Lota 

 maculosa were all small, fragmentary and mostly immature. The dimensions 

 are according to Luhe (1910:27) about 300mm. in length by about 1.5 to 3.5 

 in breadth; to Zschokke (1884:23) 350 by 4mm.; and to Ariola (1900:435) 

 250 to 400 by 2 to 4mm. Thus it is seen that as regards size the two forms 

 are more nearly aUke in Europe than here. Consequently one is not surprised 

 to read in the comparison by Zschokke, "En efifet je trouvais souvent dans le 

 meme poisson, meme dans le meme appendice pylorique des exemplaires dont 

 les uns se rapprochaient evidemment du Bothriocephalus proboscideus, tandis 

 que les autres presentaient les caracteres de Vinfundibuliformis. Souvent 

 aussi les caracteres des deux especes etaient reunis sur un seul individu, par 

 exemple le cou assez prononce avec des proglottis en forme de batons, ou point 

 de cou avec les proglottis infundihulijormes bien caracterises. " 



In preserved material the scolex assumes a great variety of shapes, from 

 the much elongated form with the *'neck" of Olsson (1893:17) and earlier 

 writers shown in figure 37, to that from Salmo salar, shown in figure 39. 

 Altho the latter is much the largest and apparently quite different from the 

 former, scolices quite like it excepting for size were seen in specimens from the 

 lake trout, and all stages between these two extremes were observed. The 

 form with the neck, it may be said, is much more common in the youngest 

 strobilas and plerocercoids (Figs. 53, 54). Regarding this structure Zschokke 

 (1884:24) said that, "a I'etat de forte contraction le cou disparait presque 

 completement. " Those from Lota mactdosa, the ling, need special mention 

 since, as shown in figure 38, the terminal disc and anterior half of the organ 

 of fixation is in many instances greatly swollen to form a sort of pseudoscolex 

 which is usually found imbedded in the walls of the pyloric ceca of the host 

 or often simply protruding into the lumina of the ceca. But this modification 

 was found only in the older strobilas; in the younger chains the scolex is as 

 sho^Ti in figures 41, 42, which are drawn to the same scale. The largest with this 

 first form of scolex was 30mm. in length by 1.2 in breadth, while the shortest 

 with the swollen end was 20 by 1.0mm. ; so that somewhere between the lengths 

 of 20 and 30mm. the imbedding of the scolex with the concomitant enlarge- 

 ment of the terminal disc takes place. Several intermediate stages were seen, 

 and the swollen scolices were varied in shape and degree of intactness. The 

 latter might seem to point to the condition being due to mechanical or physical 

 means, but this is offset by the fact that the material was in good histological 

 condition when sectioned. 



The segments also vary considerably in shape, the first ones being in speci- 

 mens from fresh-water hosts distinctly cuneate or infundibuliform and sHghtly 

 broader than long, the middle ones relatively broader and shorter, and the 

 posterior segments especially in the older chains very short and crowded. 

 Furthermore, in larger and older strobilas of the fresh-water form the posterior 

 kind of segment, that is, the very short broad form, is found relatively farther 

 forward, and the hinder end of the same quite similar, excepting for size, to 



