PARASITIC FLATWORMS 431 



of a rosette. Eggs thin-shelled, without lid. Embryonal development in uterus; all eggs of 

 an entire worm may be in many cases at the same stage of development, at a given season. 

 Liihe makes two subfamilies, Ptychobothriinae and Amphicotyhnae. 



11 (12) Genital pore on surface of proglottid. 



Bothriocephalus Rudolph! 1808. 



Scolex distinctly elongated, bothria not well developed. External segmentation incomplete 

 between successive proglottids; serrate marginal incisions distinct but markings on surface of 

 proglottids often imperfect or wanting. Vitellaria in cortical layer, continuous from pro- 

 glottid to proglottid, as are also testes. No seminal receptacle. Beginning of uterus a con- 

 voluted canal (uterine duct) which opens into spherical uterine cavity. Uterine pore median, 

 ventral; orifice of cirrus and vagina median, dorsal. 



Many entries under this name really belong in other genera of the family. A revision of 

 the group is necessary before one can say which are true species of this genus. 



12 (n) Genital pore at margin of proglottid. 



Abothrium van Beneden 1871. 



Scolex not elongate, with two bothria powerful but not deep. Segmentation uncertain 

 among older proglottids because of surface wrinkles; even oldest proglottids much broader 

 than long. Nerve trunks near margin, dorsal to cirrus and vagina. Testes exclusively be- 

 tween nerve cords in two lateral fields. Vitellaria irregular, also in two broad lateral fields, 

 mostly between longitudinal muscle bundles, separated at proglottid limits. Ovary 

 reniform, ventral, median. Shell gland dorsal to ovary. Uterine sac in ripe proglottids 

 filling almost entire medullary region. Uterine pores ventral, in median longitudinal furrow 

 on strobila. 



Representative North American species. 



Abothrium crassum (Bloch) 1779. 

 Reported from salmon in Lake Sebago, Maine; not uncommon in the Great Lakes trout. 



13 (10) Orifice of cirrus and vagina on same surface as uterine pore and an- 



terior to latter or marginal. Eggs thick-shelled, with lid. 



Family DIPHYLLOBOTHRIIDAE Liihe 1910 .. 14 



Scolex and sucking organs variable in form, or replaced by pseudoscolex. Segmentation 

 usually distinct. Receptaculum seminis sharply set off from vagina near inner end. Uterus 

 long, convoluted tube, in form of central rosette; without uterine sac except in Haploboth- 

 rium. Eggs thick-shelled with lid. 



14 (27) Genital pore on surface of proglottid 15 



15 (24) All genital pores exclusively on one and the same surface of the 



strobila 16 



1 6 (19) Scolex very short, not set off from the rest of the worm. 



Subfamily LIGULINAE Monticelli and Crety 1891 . . 17 



Scolex roughly triangular, more or less drawn out to a point with contraction of worm. 

 Bothria median, small, weak. Genital organs in adult fully developed just behind scolex. 

 Testes form dorsal layer in lateral fields of medullary parenchyme. Yolk follicles in lateral 

 part of cortical area. Ovary median, ventral; shell gland median, dorsal. 



Adult in intestine of water birds; larva in body cavity of teleosts, attaining full size and 

 forming advanced rudiments of sexual organs, found occasionally in water, having been set 

 free by rupture of abdominal wall of intermediate host. 



17 (18) External evidences of proglottid formation limited to anterior end or 



entirely lacking Ligula Bloch 1782. 



When fully grown jointed only at anterior end, but the divisions do not agree with the in- 

 ternal segmentation of reproductive organs. Bothria poorly developed. Larvae without 

 segmentation and without bothria, live chiefly in Cyprinids. Adults in water birds; stay in 

 definitive host only brief. 



Several species have been reported and described by various authors, all too briefly to permit 

 of positive identification. The parasites come from chub, sucker, and trout; New York, 

 Pennsylvania, Maryland, Yellowstone Park, Arizona. 



