PARASITIC FLATWORMS 



425 



tissue of the host. In some tapeworms the head carries long suck- 

 ing grooves or bothria, and in others round cup-shaped suckers or 

 acetabula. More compUcated hold-fast organs are developed on 

 the scolex in certain groups of cestodes parasitic in marine hosts. 

 A slight constriction behind the head has been given the name of 

 "neck"; many cestodes have no neck. The body usually in- 

 creases in caliber from the head toward the opposite end. The 

 partition lines of proglottids are at first very indistinct, and be- 

 come more marked as one goes backward along the chain. The 

 form of the proglottids also changes from the scolex toward the 

 other end of the worm. Much has been made of these and other 

 minor details of external 

 appearance in the descrip- 

 tions of cestodes. They 

 are not adequate for the 

 determination of many 

 species and moreover are 

 not of fundamental signifi- 

 cance. Unfortunately very 

 few cestodes are transpar- 

 ent and it is not easy to 

 study the internal struct- 

 ure, since the specimen 

 must first be subjected to 

 a time-consuming technic. 

 Methods for the prepara- 

 tion of cestode material 

 were outlined briefly in the 

 general section of this chap- 

 ter (page 368). Specimens 

 must be kept flat and ex- 



fprirlprl or fhpv arp rUffirnlf- Ftg. 730. Ophiolaenia filaroides. Mature proglottid, un- 



lenaea or iney are amiCUlC flattened, showing relationships of organs. Abbreviations 



toc:^-nrl■^r cinrl int/^^rnrpt- r~nr us^d in thisand followingfigures: d, cirrus; a>, cirrus-pouch; 



SLUUy emu lllucipiCL l,ui de/, vas deferens; ((;, ductus ejaculatorius; e/, vasa efferentia; 



■ 1 em, excretory vessel, ventral; »(, lateral nerve; 00c, oocapt; 



reCtly. m, ovary; ut, uterus; ra, vagina; vi, vitellaria. X 52- (A£- 



T-, , 1-1 , ter La Rue.) 



Each proglottid may be 

 considered as a unit of structure as it contains a complete set of 

 reproductive organs (Fig. 730). With rare exceptions tapeworms 



