THE ACTIVE SCOLEX. 83 



The transformation of the platycercal forms into mature Ces- 

 todea takes place exactly like that of the cysticercal forms ; in 

 the acercal forms no casting off of a portion of the former 

 embryonal vesicle takes place, but the whole of it is retained, 

 and the formation of segments commences immediately upon 

 it. 



However, it is as well (if it be desired to obtain various 

 results from the administration), to remove the worms from 

 their envelopes, and to make an incision into those which possess 

 very large vesicles, as when uninjured they are very easily vomited. 

 The teeth of the predaceous animal are sure to injure the larger 

 vesicular worms, sucli as Echinococcus and Cysticercus tenuicollis. 



In nature we only find the tape-worms in question in animals 

 which live in freedom, and which can get freely at the animals 

 infested with cystic worms. Animals kept constantly chained 

 up, or in rooms, stables, &c, and fed only with boiled, baked, or 

 dry food, do not bear in their intestines even the tape-worms 

 which occur in free animals of their species, any more than the 

 vesicular worms which are found external to the intestine in the 

 latter. The circle of animals in the intestine of which a par- 

 ticular species of vesicular worm thrives, is not usually large. 

 When experiments in the administration of cystic worms are 

 made, any diarrhoea which makes its appearance in the animals 

 experimented on must be quickly stopped by opiates. Irritation 

 of the intestines, and especially diarrhoea, destroy the results. 



From the moment at which the extended cystic worm has 

 attached itself in the intestine — and begun to derive its nourish- 

 ment therefrom, when at the same time certain changes take 

 place in its body and caudal vesicle, which, for example, is rup- 

 tured — commences the transition into the last stage, and a crea- 

 ture of this kind may certainly be called a young Tamia. Thus 

 we speak at once of a butterfly when the animal which was 

 previously inclosed in the pupa case bursts its envelopes, and 

 issues into a new medium, the open air. Freedom in an open, 

 free space, change of medium, and the altered and more active 

 vital phenomena of the animal, which it acquires in order to seek 

 voluntarily for its own nourishment, constitute the change from 

 a pupa to a butterfly, and the same things render a cystic worm 

 a true young Tcenia, whether it still bears behind it its caudjil 

 vesicle for the moment, in the same way as the young chick its 

 egg-shell, or has already cast off this and commenced its further 



