192 ILUNOIS BIOLOGICAL MONOGRAPHS [480 



breadth and about 2min. in thickness. One from Caregonus clupeijormis 

 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 Liihe (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 alike in Europe than here. Consequently one is not surprised 

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

 m^me poisson, m&ne dans le mSme appendice pylorique des exemplaires dont 

 les uns se rapprochaient evidenmient du Bothriocephalus proboscideus, tandis 

 que les autres presentaient les caract^res de Vinfundibuliformis. Souvent 

 aussi les caracteres des deux esp^ces etaient reunis sur un seul mdividu, par 

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

 de cou avec les proglottis infundibulifomus bien caracterisfe. " 



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

 the much elongated form with the "neck" of Olsson (1893:17) and earUer 

 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, "k I'^tat de forte contraction le cou disparalt presque 

 compl^tement. " Those from Lota maculosa, 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 

 shown in figures 4 1 , 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 oflFset 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 slightly 

 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 



