132 



THE CESTOIDEA 



admirable text-book, while those infesting domestic animals are 

 described in Raillet's TraiU de Zoologie, medicale et agricole. 



Certain fresh-water fish are inhabited by certain species of 

 Taenia (s. 1.), as well as by the genus Ichthyotaenia, and various 

 species of anurous Amphibia by T. dispar. Birds are attacked by 

 members of a special family, the Ecliinocotylidae, as well as by species of 

 Dr&panidotaenia, provided with a powerful armed rostellum, but the 

 majority of species occur in Mammalia. Although in higher forms 

 the parasite is confined to a single host, or to closely allied hosts, in 



FIG. XXII. Peculiar scolices of Tetracotylea. a, acetabulum ; b, rostellum, or its 

 representative ; c, expanded region. 



1, 2. Corallobothrium lobosum, Rigg., out of Pimelodus pati (after Riggenbach) ; side view ; 

 and viewed from above (compiled from Riggenbach's descriptions and figures). c, the 

 notched lobes rising up from below the scolex and hiding it ; d, groove between them. 



3, 4. Sciadocephalus megalodiscus, Dies., out of Cichla monoculus (after Diesing); side view 

 and top view ; c, disc-like expansion of the scolex. 



5. Parataenia medusia, Lint., out of Trygon centrum (probably synonymous with Polypo- 

 cephalus, Braun). b, the sixteen rostellar tentacles, capable of retraction, into a cavity in 

 the scolex. 



6. Anoplocephala perfoliata, Goeze, out of the caecum of horse (after Raillet). e, peculiar 

 ear-like flap, regarded as homologous with the phyllidium of Tetraphyllidea. 



7. Davainea echinobothrida, Megn., out of Gallus domesticus (after Megnin). The armed 

 rostellum is indicated in a retracted condition. A, rostellar hooklet ; B, acetabular hooklet. 



those inhabiting fish, birds, the same parasite occurs in numerous 

 hosts, and vice versa, one host contains numerous species of Cestodes. 



In this order of Cestodes the organs of the scolex are true 

 suckers (acetabula), the structure of which closely agrees with those 

 of Distomid Trematodes. Each is a deep, hemispherical, or sub- 

 spherical cup, hollowed out in the side of the scolex, with circular 

 (Taenia), oval, or even slit-like openings (Moniezia). No fusion of 

 these suckers occurs, and it is quite exceptional that they are 

 armed with booklets (Echinocotylidae). 



A new light has recently been shed upon the homologies of 

 these organs by Pintner (34, b), who adduces evidence to show 



