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, which 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 livmg independently as Tre- 
matodes, but are the analogues of complete or adult Meduse 
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 Planaria, 
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 phzenomenon. 
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 
