PHYLUM PLATYHELMIKTHES 



255 



forms between the two classes, the shape of the average Cestode 

 is very different from that of such an average Trematode as the 

 Liver-Fluke. The body of an ordinary Cestode is of great length 

 sometimes extending even to a good many feet and relatively 

 narrow, being compressed into the form of a ribbon. One end. 

 which it will be 

 convenient to 

 designate ante- 

 rior (though it 

 may not, per- 

 haps, correspond 

 to the anterior 

 end in a Trema- 

 tode or a Turbel- 

 larian), is, in 

 most cases, at- 

 tached to the 

 host by means 

 of suckers and 

 hooks placed on 

 a rounded lobe, 

 the head or 

 scolex, connected 

 with the body 

 by a narrow part 

 or neck. The 

 head is usually 

 rather radially 

 than bilaterally 

 symmetrical, 

 with four suckers 

 and a 'circlet of 

 hooks. The 

 hooks, when pre- 

 sent, are borne 

 on a longer or 

 shorter retractile 



process, 



the 



TOS- 



EIG. 204. Temnocephala minor, general view of the 

 organisation, c. cirrus ; e. s. ejaculatory sac ; g. c. genital 

 atrium ; t. intestine ; o. germarium : oo. ootype ; ph. pharynx ; 

 pr. prostate glands ; r. d. strands of ducts of integumentary 

 glands running forwards to the tentacles ; r. g. groups of inte- 

 gumentary (rhabdite-forming) glands ; r.v. receptaculum ; s. 

 sucker ; t. testes ; te. tentacles ; t. s. terminal sacs of excretory 

 system ; v. s. vesicula seminalis. 



tellum, the long 



axis of which is 



in line with the 



long axis of the 



body. In Bothriocephalus and allied forms a pair of longitudinal 



grooves take the place of suckers, and there are no hooks. In many 



Cestodes parasitic in Fishes the head bears four prominent, thin, 



folded flaps the bothridia, which are exceedingly mobile, and are 



used more as creeping organs than as organs of fixation. In relation 



