192 



PLATHELMINTHES 



The class contains not far from 1,000 species, which are distributed 

 among 2 subclasses. 



Key to the subclasses of Cestodes: 



Qi No scolex ; no segmentation ; embryo with 10 hooks 1. Cestodaria 



tti Body usually segmented and with a scolex ; embryo with 6 hooks. 



2. Cestodes, s. sir. 



Subclass 1. CESTODAEIA. 



Small, unsegmented worms which live in fishes as adults and in 



mollusks and annelids as larvae; no distinct scolex is present although the 



forward end has a contractile papilla or a sucker ; but 1 set of genital organs 



present; uterus a winding tube with an external opening; embryo with 10 



locomotory hooks and called a lycophora: 2 genera and about 4 species. 



1. Gyrocotyle* Diesing (Fig. 312). Body leaf-like and elliptical, 



with fluted margins; a small sucker at one end and a peculiar ''rosette'' 



organ at the otlier end with a retractile proboscis: 4 



species. 



G. fimbriata Watson. Length up to 55 mm. ; width 

 10 mm.; in intestines of Chimcera; California. 



2. Amphilina Wagener. Body flat and leaf-like: 

 forward end with a small sucker, beside which is the 

 uterine pore; at the opposite end are the openings of 

 the cirrus and the vagina: 2 species. 



A. foliacea (Rudolphi). Length 20 mm.: in the 

 body cavity of sturgeons. 



Subclass 2. CESTODES— /S'ensit stricto. 



Fig. 312 

 Diagram of 

 Oyrocotyle 

 (Spencer from 

 Watson). 

 1, sucker ; 2, male 

 genital pore ; 3, 

 vaginas 4, uter- 

 ine pore; 5, 

 nerve : 6, uterus ; 

 7, yolk duct ; 8, 

 rosette. 



Body, except in rare cases, segmented, with a 

 scolex, which, however, may be rudimentary or re- 

 placed by a pseudoscolex ; uterus with an external 

 opening only in the Botliriocephaloidea; vas deferens 

 and vagina open usually into a genital cloaca which 

 opens to the outside by a single pore: 5 orders and 

 about 90 genera. 

 Key to the orders of Cestodes here described : 

 Oj Uterine pore present; genital organs do not degenerate in the ripe seg- 

 ments 1. BOTIIRIOCEPHALOIDEA 



02 No uterine pore ; ripe segments contain the gravid uterus and little else. 

 bi Proboscides not present in scolex. 

 Ci Four bothria usually present ; yolk ghinds paired ; principally in fishes. 



2. Tetkaphyllidba 

 Co Four suckers present ; yolk glands not paired ; in land vertebrates. 



3. Cyclophyllidba 

 62 Four retractile proboscides present in scolex ; in fishes. 4. Trypanorhyncha 



* See "The Genus Gyrocotyle," etc., by E. E. Watson, Univ. of Cal. Pub., Vol. 6, 

 p. 353, 1911. 



