13G 



HELMINTHOZOA. 



Fig. 70. 



the Scolex of the other. Siebold had, indeed, satisfied himself that the 

 arrangement of the horny circlet of Cystwerciis fasciolaris, found in the 

 liver of the mouse, entirely corresponded with that of Tcmia crassicollis, 

 that inhabits the intestines of the cat. If young TaBnias and Cysticerci 

 he carefully examined, and compared with other forms, it is satisfactorily 

 seen that the Cysticercus is merely the Scolex from which a Trenia may 

 be developed, and that its vesicular portion corresponds exactly with the 

 similar vesicles of some Tetrarhynchi in a like state of development. A 

 Taenia, says Van Beneden, might probably very well acquire its com- 

 plete development, without assuming the vesicular form, as is proved 

 by the Paradoxical TaBnia ; but, for that, it would be necessary that the 

 germ should be deposited in an intestinal tube. The same is the case 

 with the Tetrarhynchi : here also the body becomes quite out of propor- 

 tion to the size of the head whilst the germ remains amongst the 

 peritoneal folds of the fishes in which they are found, just as the 

 Cysticerci do whilst imbedded in the peritoneum or amongst the 

 muscles. The Scolex, when fully formed, has its own individual de- 

 velopment arrested at this point ; but it now begins to give off buds, of 

 which the body (Strobile) of the Entozoon is composed. 



(351.) The Scolex, therefore, in this stage of development is syn- 

 onymous with the " head," or, as it 

 might as well be called, the " root " 

 of the worm ; and as long as this root, 

 head, or Scolex remains unexpelled 

 from the body, it will continue to give 

 origin to fresh segments or joints, ad 

 libitum. 



(352.) Gradually the tail of the 

 Scolex, or the body of the worm, is deve- 

 loped ; and as soon as this has attained 

 a certain length, transverse markings 

 begin to make their appearance, seg- 

 ments are formed, separated from each 

 other by slight indentations, and the 

 internal organs appropriate to each 

 segment are progressively evolved. 

 When the segments have attained to 

 maturity, or, in other words, when 

 the gemma has grown into an adult 

 worm (Proylottis of Van Beneden), 

 the indentation separating each from 

 the one preceding it increases in 

 depth, until, being reduced to a mere 

 pedicle, the segments are successively thrown off as so many distinct 

 animals. From the above account, therefore, it is evident that the last, 



, Scolex ; bed, Strobile ; e, Proglottis. 



