CESTODA. 657 



ferred to the alimentary canal of its final host, either the region of the neck 

 may lengthen, sets of generative organs appear, as well as a more or less dis- 

 tinct division into joints, and with the liberation of the first formed joints 

 the proscolex may also be set free, as mLigula and fish tapeworms, &c. ; or 

 else, as most commonly occurs, the proscolex is digested in the stomach of 

 the host and the scolex, passing on into its intestine, affixes itself, the neck 

 lengthens, generative organs and joints appear. The view that proscolex 

 and scolex are parts merely of a non-sexual worm which becomes sexual 

 on transference to a new host is more probable than that there is an Alter- 

 nation of Generations, including either three individuals, the non-sexual (i) 

 proscolex and (2) scolex, with (3) the sexual joints ; or two, (i) the non- 

 sexual proscolex, and (2) the scolex, which becomes sexual in the second 

 host ; see pp. 232-3 \ 



The scolex is rarely devoid of all organs of adhesion, as in Caryo- 

 phyllaeus, Leuckartia^ and Abothrium Gadi. Suckers are usually present. 

 There is a single terminal sucker resembling the oral sucker of a Distome 

 in the Amphilinidae ; there are two lateral cephalic grooves in all Psetido- 

 phyllidea which are produced in Solenophorus and Duthiersia into 

 cornucopia-like structures with basal perforations. Echinobothrium has 

 two flattened suckers, but in other Cestoda there are four, cup-like in 

 Taeniadae and Tetrarhynchus \ large, extremely mobile, and crisped mar- 

 ginally in some Phyllobothriums, e. g. Phyllobothrium lactuca ; areolate as 

 in Calliobothriuin, or pedunculate as in Anthobothrium ; whilst Polypoce- 

 phahis, from the intestines of an East Indian Rhinobatis, has the anterior ex- 

 tremity surrounded by sixteen hollow (?) muscular tentacles, as well as armed 

 with two or four suckers. Chitinoid hooks are present in some Taeniadae, 

 in Tetrarhynchidae, Phyllacanthinae, Echinobothrium, and Triaenophorus. 

 They are disposed in one or more circles round the base of a rostellum or 

 central projection from the head in Taeniadae ; in numbers upon four con- 

 tractile proboscides, with which the head is furnished in the Tetra- 

 rhynchidae ; and on the upper part of the suckers in the Phyllacanthians 

 and Echinobothrium. The last-named is remarkable for also possessing 

 three longitudinal series of hooks on each surface of the neck. The hooks 

 are curved, e. g. Taeniadae ; forked, e. g. Aeanthobothrium ; straight, 

 Echinobothrium ; implanted by large and forked roots in the Taeniadae, 

 and moved by special muscles 2 . 



The neck and body of the worm are more or less flattened. One sur- 



1 The life history of the non-segmented genus Caryophyttaeus is not known. It may be noted 

 that it has recently been asserted that Taenia serrata may undergo its development within the intestines 

 of one and the same host ; but the evidence is not conclusive, and such an occurrence is not probable. 



2 Taenia eehinobothrida (Megnin) from the Fowl and wild and tame Pigeons has the four 

 suckers covered with minute hooks. According to the same authority, hooks, suckers, and even the 

 scolex may atrophy when sexual maturity is attained. See on both points, Journal de 1'Anat. et 

 Physiol. xvii. 1881. 



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