CESTODA. 787 



It must be allowed that the process of development ahove 

 recorded is one of the most astonishing of all the biological pheno- 

 mena with which the naturalist is acquainted. Not merely are 

 the necessary changes of host remarkable, but the characteristics 

 marking each phase in the life-history of the entozoon itself are 

 still more noteworthy. At one time of its career the creature is 

 a mere bladder-worm, at another an elongated tape-worm, at 

 another a minute six-hooked embryo, and finally, once more, a 

 bladder- worm. But this is not all ; inasmuch as its develop- 

 ment, in one very important particular, differs from the process 

 undergone by the ordinary beef and pork tape-worms {Tcenia 

 riiediocanellata and Taenia solium). Thus, whilst the egg of 

 the common tape-worm is only capable of developing onward 

 into a single sexually mature tape-wqrm, the solitary egg of the 

 Tmnia ccenurus, as we have seen, becomes transformed into a 

 multitude of tape- worms. In this respect, it is true, our parasite 

 is, in some sense, eclipsed by another tape-worm that is resident 

 in the dog {Tcciiia echinococcus) ; but, with this exception, we 

 know of nothing comparable to it within the limits of cestode 

 reproduction. 



Amongst the other tape-worms of general interest to the pro- 

 fessional man are those which are derived from the consumption 

 of pork and beef The measles of pork {Cysticercus cellulosiis) 

 are transformed into the Tcenia solium, whilst those of beef 

 {Cysticercus hovis) are transformed into the Tcenia mcdiocancllata. 

 These tajDC-worms, as such, are only known to infest the human 

 body. The tape-worms of cattle and sheep, as well as those of 

 the horse, probably all belong to that group of tape-worms whose 

 larvse are normally resident in the bodies of insects and other 

 non-vertebrated animals. This explains why their separate 

 developmental histories have not hitherto been fully made out 

 by helminthologists. 



Those who desire further details on this head should consult 

 the standard treatises of Leuckart and Kiichenmeister, and 

 also Cobbold's manual of the parasites of our domesticated 

 animals, in which the medical and sanitary importance of the 

 beef tape- worm is dwelt upon at considerable length. Lastly, 

 we desire to call particular attention to the fact that cysticerci 

 or measles have been found in mutton. These small cystic 

 worms are undoubtedly the representatives of a distinct species 



