CESTODES 193 



ORDER 1. BOTHRIOCEPHALOIDEA. 



Body often long, with or without distinct segmentation; scolex with 

 2 suckers, one in the dorsal and one in the ventral surface, which are 

 usually weak and in certain forms are highly modified by the extension of 

 their edges, and may be rudimentary or wanting, when their place may 

 be taken by a single accessory sucker or 'a pseudoscolex ; a uterine or 

 birth pore present in the ventral surface; the other two genital pores 

 also usually ventral but may be dorsal or marginal; testes numerous; 

 ovary either distinctly or indistinctly paired and in the hinder part of 

 the segment ; yolk glands paired in the lateral areas of the segment ; the 

 genital organs do not degenerate: about 4 families; either adult or larval 

 form usually in fishes. 



Key to the families of Bothriocephaloidea here described: 



01 Uterus an irregularly coiled tube 1. DIPHYLLOBOTHRIIDAE 



o a Uterus not a coiled tube, usually sac-like 2. PTYCHOBOTHRIIDAE 



FAMILY 1. DIPHYLLOBOTHEIIDAE. 



Scolex usually without hooks, segmentation in most cases distinct, 

 but sometimes wanting; cirrus (penis) without spines; uterus a long tube 

 coiled back and forth across the segment: 4 subfamilies and about 15 

 genera. 



Key to the subfamilies of Diphylloboihriidae here described: 



Ox Two suckers present. 



&! Scolex very short ; no neck present 1. LIGULINAE 



6 2 Scolex elongate ; neck usually present 2. DIPHYLLOBOTHRIINAE 



2 But 1 sucker 3. CYATHOCEPHALINAE 



SUBFAMILY 1. LIGULINAE. 



Scolex short, triangular, with small suckers and without hooks ; genital 

 pores ventral : in the intestine of water birds as adults ; larva a plerocer- 

 coid which may be as large as the adult and is found free 

 in the body cavity of fishes : 2 genera. 



1. LIGULA Bloch. Suckers and external segmentation 

 wanting in the larva, and only the forward portion exter- 

 nally segmented in the adult, these segments, however, not 

 corresponding to the internal segmentation: 1 species. 



L. intestinalis (L.) (Fig. 313). Length up to 40 cm. or 

 more ; width 10 mm. : in perch, pike, and other fresh-water 

 fish as a larva, and in gulls and other water birds as 

 adult. 



2. SCHISTOCEPHALTTS Creplin. Suckers and external segmentation 

 present and distinct in the larva as well as the adult, and internal and 

 external segmentation identical: 1 species. 



