84 ANIMAL PARASITES. 



development. Von Siebold has objected to this nomenclature, 

 and thinks that, " in this case all that is necessary is to press out 

 the head of the vesicular worm, and the transition to Tsenia-life 

 is effected." I am no friend to sophisms and word-siftings, but 

 I think that when a comparison is to be made, the cardinal 

 points of the comparison must be retained, and whether I or 

 Von Siebold have missed the analogy, I shall leave to others 

 to decide. We have seen that the cystic worm keeps its head 

 still retracted whilst in the stomach, or if it is protruded it is 

 soon retracted again, and the books are not turned out so as to 

 adhere, but retracted, and their apices directed backwards and 

 inwards, and their shafts forwards and outwards. As long as 

 the worm keeps its hooks in this position, no one will call it a 

 Tcenia, even if it should have elongated its body and neck. 



We have still the last question to consider How does the 

 scolex, after entering upon its activity, become converted into a 

 tape-worm colony = Strobila ? and for this purpose we must regard 



V. The Strobila = the so-called tape-worm colony. 



Immediately after the healing of the cicatrix on the neck, and 

 on the former receptaculum capitis, there commences, between 

 the posterior end of the head and this cicatrix, a budding forth 

 of the body, produced without sexual propagation, and which 

 becomes constricted into segments by transverse furrows or 

 wrinkles. By the constant production of new masses on this 

 place, that previously formed is continually pushed further back, 

 so that this cicatrix is at last removed to a considerable distance 

 (varying according to the species) from the head. During this 

 time the individual divisions and segments increase and grow in 

 the same ratio as their removal from the head ; they at the same 

 time acquire sexual organs, male and female, in each seg- 

 ment, and which are very rarely (if O. Schmidt's observation 

 on the Tcenia dispar of the Frog 1 should be confirmed, and 

 the spermatozoids have not been overlooked), and probably 

 never entirely wanting in the colony. Finally, when they have 

 attained a sufficient size and maturity, they produce the embryos 

 (Section II), and last of all cast themselves free in the form of the 



1 'Ueber den Bandwurm der Frosche, Tcenia dispar, und die geschlectslose Fort- 

 pflanzung seiner Proglottiden,' Berlin, 1855. 



