128 THE CESTOIDEA 



The metacestode phase is a cysticercoid, the head Avith its 

 apparatus being enclosed in a bladder similar to that of Tetra- 

 phyllidea ; this occurs encysted in various tissues, especially the 

 wall of the gut, of Teleosteans, or with everted head, free in the 

 alimentary canal of sharks. The bladder may be a foot or more 

 in length, as T. elongatus, T. macrurus. The adults of some species 

 were observed by v. Beneden with this " bladder " attached at the 

 end of the strobila. 



The scolex may after e version separate from the bladder, and 

 in this condition has been found in Sepia (as T. sepiae). 



The cysticercoid, with the enclosed scolex, was known as Flori- 

 ceps (Cuv.), and as Anthocephalus (Rud.), and the term Tetrarliynclms 

 was applied to the stage with everted scolex ; van Beneden showed 

 that these are merely stages in the life-history of the strobila known 

 as Rhyncliobotlirium. It is still undecided amongst systematists 

 which of these two last names should be used. 



ORDER 4. Tetracotylea, Dies. ( = Taeniidae, auct). 



Tetrabothridiate Merozoa, in which the organs of the scolex have the 

 form of cup-shaped or hemispherical " acetabula " hollowed out in the sides 

 of the scolex, and without projecting or mobile margins. 1 Booklets are 

 rarely present in these acetabula. There is usually a rostellum, which may 

 be armed with a crown of hooklets. Members of the order are mostly 

 parasitic in warm-blooded vertebrates. FAMILY 1. ICHTHYOTAENIIDAE, 

 Lonnberg. The sucking organs are acetabulate, but the generative organs 

 resemble those of the Tetraphyllidea. 2 Ichthyotaenia, Lonnb. ( = Tetracotylus, 

 Montic.) ; several species in fresh-water fish (see 10 and 37). Corallobothrium, 

 Fritsch (Fig. XXII. 1). FAMILY 2. ECHINOCOTYLIDAE. The acetabula are 

 armed ; rostellum with one or two circlets of hooklets ; parasitic in birds. 

 Echinocotyle, Blanch., a single crown of hooklets, which are falciform. 

 E. rosseterij Blanch., in the duck ; " metacestode " in Cypris cinereus. 

 Davainea, Blanch, and Raillet (Fig. XXII. 7) ; D. proglottina, Dav., with 

 four proglottids ; fowl and slugs. D. contorta, Zscli., from Manis 

 pentadactyla. Cotugnia, Diam., with two sets of genital organs in each 

 proglottid. Idiogenes, Kr. ; Ophryocotyle, Friis. FAMILY 3. TAENIIDAE. 

 Scolex globular or pyriform ; suckers unarmed ; rostellum may or may 

 not be armed ; vagina elongated, posterior to the cirrus ; mostly parasitic 

 in mammals ; larval stage a "cysticerctis " or "cysticercoid." SUB-FAMILY 1. 

 HYMENOLEPINAE (= Cystoidea, Lkt). Strobila of moderate or small 

 size ; scolex with one, two, or several circles of hooklets ; eggs with 

 transparent, multiple envelopes ; larva, a cysticercoid in Arthropods and 

 Mollusca. Dipylidium, Lkt., rostellum armed with peculiar hooklets, like 



1 In some avian tapeworms living in Apteryx the lower margin projects slightly 

 and may he mobile (Benham, Q. J. M. Sc. xliii. 1900, p. 83). 



2 The gemis Sciadocephalus, Dies. (Fig. XXII.), is doubtfully placed here. It is by 

 some authorities put in the family Gamobothridae, among the Tetraphyllidea. The 

 family Ichthyotaeniidae, in fact is possibly a member of the latter order. 



