500 DEVELOPMENT AND GROWTH OF TAENIA SOLIUM. 



of which it finally develops by increase of size and formation of the 

 head into the familiar bladder-worm. 



The observations on which these statements are based relate only 

 partially to the bladder-worm of the pig. The later stages have been 

 correctly determined, but the first phases do not belong at all to the 

 development of the bladder-worm. They are connected with an 

 entirely different parasitic form, namely, with those organisms which 

 we designate as Miescher's tubes, and rank along with the Psorospenn- 

 saccules.^ In the first edition of this work^ I proved their identity 

 with the forms discovered by Miescher and Hesshng. Subsequent 

 investigators have confirmed this, so that Eainey's reports do not 

 require further refutation. The mistake will, however, be readily 

 excused by all who know the difficulty of the problem. 



Gerlach was no more fortunate than I was in his search for the 

 youngest stages of the bladder-worm. In a young pig which died of 

 intestinal inflammation nine days after feeding, no trace of the infec- 

 tion was to be seen. It was different, however, in the case of a young 

 pig which died, without apparent external cause, twenty-one days 

 after feeding. Here there were in the flesh numerous dehcate bladder- 

 worm vesicles, transparent, and therefore difficult to detect. They 

 had no enveloping membrane, were about the size of a pin's head, 

 and exhibited a minute transparent point, the first rudiment of the 

 head.^ 



Even before Gerlach, I found* in the muscles of a young pig (which 

 had been fed twenty-one days before with about eighty proglottides) 

 young bladder-worms in the form of thin- walled, free vesicles of at 

 most 0'8 mm. in size. They had a spherical form, but were occasionally 

 somewhat narrowed towards the head-rudiment, and provided with a 

 thick border, from which the former projected like a wart. There was 

 no proper cavity to be seen inside, although the cuticle was already 

 somewhat invaginated at the point of attachment. Vessels could not 

 be detected with certainty. 



In addition to these developmental forms, I observed others 

 thirty-two days after the last feeding. They occurred in a young pig 

 which had devoured an immense number of ripe proglottides forty 

 days before dissection. 



The smallest bladder-worms found were vesicles 1 mm. long by 

 07 broad. They lay for the most part in the muscles, but there were 

 some also in the liver and brain. A proper capsule was present only 

 in those found in the liver. Those in the muscles indeed were also 



1 See p. 199. '^ First German edition of this work, p. 238. 



* Loo. cit., p. 66. ■* Loc. cit., p. 745. 



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