THE CYSTIC ENTOZOA. 47 



CHAPTER III. 



ON THE CYSTIC ENTOZOA. 



ZOOLOGISTS have hitherto founded the genera and species of 

 Cestoidea on the characters presented by the head and by the 

 fully developed joints only ; and even these characters have been 

 but superficially and imperfectly employed, so that a close 

 revision of this order of Entozoa has long been necessary. This 

 task has been recently undertaken by Diesing and by Van 

 Beneden, but the labours of these two helminthologists have led 

 them to very different results. The great point in revising the 

 old genera and species of the Cestoidea is, to discover what forms 

 of proglottis belong to certain scolices which are commonly found 

 without proglottides (and which, therefore, have long been 

 regarded as distinct genera of Cestoidea}, and to unite these 

 together. Diesing has not attempted to do this, having appa- 

 rently no conception of the bearing of the alternation of gene- 

 rations upon the systematic arrangement of the lower animals. 



On the other hand, Van Beneden, guided by the light of the 

 alternation theory, has justly recognised and given due promi- 

 nence to, the affinities of certain Cestoidea. To this end the 

 different kinds of scolex require to be more carefully defined 

 than they have hitherto been, and the use of the microscope 

 becomes indispensable. The forms of the apparatus of attachment 

 must be determined and compared with the utmost care, and 

 those hooks and protractile proboscides, armed with more or less 

 moveable booklets, which are attached to the head of the scolices, 

 are especially adapted, from their varying and well marked figure 

 and disposition, to afford good generic and specific characters. 

 If the form and arrangement of that apparatus of attachment of 

 the Taeniadan which is known as the circlet of hooks, of the 

 proboscis which carries it, and of the sac which conceals it, had 

 been carefully observed, the identity of many so-called species of 

 Taniadce would long since have been recognised, and the close 



