48 THE CYSTIC ENTOZOA. 



relation of the Cystica with the Cestoidea would not have been a 

 recent discovery. It must not be forgotten, however, that in 

 very many Taniada, the scolices lose their circlet of hooks with 

 advancing age, and that in many Cestoidea, the suckers of the 

 scolices undergo great changes of form when the development 

 of proglottides commences ; in consequence of which it is often 

 very difficult to demonstrate the connection of the older and 

 younger individuals of one and the same species of cestoid. 

 The proglottides of the Cestoidea, again, considered as individuals 

 wholly separate from the parental organism, present distinct 

 specific characters, though they are not, perhaps, very obvious 

 at first sight. In these it is the sexual apparatus more par- 

 tictdarly which, forming as it does the principal mass of the 

 proglottis, presents excellent specific characters, in the form, 

 dimensions, number, and arrangement of its parts. Van Beneden 

 has the merit of having paid particular attention to these par- 

 ticulars in distinguishing the different species of proglottis. 



As I have already hinted, the cystic worms, which were made 

 by Rudolphi into a distinct order of Entozoa, are so closely 

 allied to the Cestoidea that they have no claim whatever to be 

 regarded as an independent group. Since, in addition, various 

 kinds of scolices have been regarded as distinct genera of 

 Cestoidea, it is high time that zoologists should resolve to erase 

 from their systematic arrangements all these groups, which are 

 in reality, based only on our ignorance of the natural history of 

 the Entozoa. How great a number of these improper genera 

 have been introduced may be judged by the fact that out of the 

 order Entozoa cephalocotylea, alone, established by Diesing, 1 and 

 containing thirty-two genera, ten genera must be eliminated, 

 namely, Echinococcus, Coenurus, Cysticercus, Piestocystis, Antho- 

 cephalus, Acanthorhynchus, Pterobothrium, Tetrabothriorhynchus, 

 Stenobothrium, Scolex. Many of the Entozoa arranged under 

 these genera are merely the scoliciform agamozooids of other 

 Cestoidea ; a fact which is demonstrated not merely by their 

 undeveloped and sexless body, but by their habitation, since they 

 are almost all found, not in the alimentary canal of a vertebrate 

 animal, but in its other viscera. Another portion of these genera 

 consists of the cystic worms, which are also nothing but the 

 scolices of certain Cestoidea, with this difference, however, that a 

 portion of their body is enlarged into a vesicle. 



1 Diesing, ' Systeraa Helminthum,' i, p. 478. 



