44 M. Van Beneden on a new genus of Cestoid Worm. 



implanted but distinct spines, directed backwards, and like those 

 of the head easily separable. 



The trunk forms the remainder of the body, made up of nu- 

 merous segments, first indicated by delicate lines, and towards 

 the posterior extremity by deep constrictions, which ultimately 

 end in transverse fission. 



The individual joints constitute the last or adult phase of the 

 worm on the completion of their development, wdiich may occur 

 before their separation from the strobiloid animal. The four 

 cords seen in the latter belong also to this third generation, which 

 however alone possesses a sexual system. * 



The development of these segments is by gemmation, differing 

 it will be found in no essential points from that in Polypes, if an 

 extended view of the process be taken. 



Third or Proglottoid generation. Along with yet entire arti- 

 culated worms, joints are met with living independently as Tre- 

 matodes, but are the analogues of complete or adult Medusa 

 derived from the fission of the Strobila. After their separation 

 from the strobiloid parent, these joints increase in size so consi- 

 derably as to equal that of two or three yet attached segments. 



They also undergo a change of form ; — losing their flat rib- 

 bon-like form, they become rounded or purse-shaped. In gene- 

 ral characters and in their movements they resemble Planarice, 

 but have been yet more frequently confounded with Trematoda. 



Their investing integument offers nothing peculiar. Its sur- 

 face presents neither cilia nor folds, but is occasionally furrowed. 

 Its continuity is uninterrupted, except at the opening by which 

 the lemniscus escapes; no mouth or respiratory organ being 

 apparent. The internal organs maintain an adhesion with the 

 external wall. 



No evidence supports the notion that the organ variously 

 called the lemniscus, cirrhus, cirrhule, and penis, belongs to the 

 reproductive apparatus ; and the observation of the passage of 

 spermatozoa by it is illusory, for we have examined this organ in 

 every stage of development, and at the period of its greatest 

 vigour, without perceiving the least indication of such a passage. 

 The anatomical character of the lemniscus is also opposed to 

 such a phenomenon. 



In our opinion this appendicular organ performs the same 

 office as the tubes of the Tetrarhynchus, viz. that of affixing the 

 animals to the tissues, or of infolding them more completely in 

 the mucus in which they live. 



Its position varies in different genera: in the Helminth in 

 question it occupies the median line about the posterior third of 

 the body. It is distinguishable when inclosed in its sheath ; is 



