OLDER VIEWS ON THE SUBJECT. 



331 



must therefore presuppose an emigration from the original host, and 

 a transference to another victim. Afterwards v. Siebold declared 

 that the embryo took the form of a tape-worm head " outside the in- 

 testine of the vertebrate host," and subsequently gained a new home. 

 He gives no hint, however, as to the manner of the metamorphosis. 

 In fact there were no direct results of observation to go upon ; all the 

 statements were more or less plausible inductions. 



Von Siebold's opinion received its first actual corroboration by an 

 observation of Stein. 1 He found in the body-cavity of Tenebrio 

 molitor and its larvae numerous 

 cysts, which exhibited a tape- worm - 

 like head enclosed in a bladder. 

 This had obviously resulted from 

 the metamorphosis of the six- 

 hooked embryo, as the six hooks 

 still adhering plainly indicated. 

 In some cysts there was only a 

 simple roundish body, without a 

 tape-worm head ; in others the for- 

 mation of the latter could be seen 

 going on within this body. As to 

 the origin of the tape-worms, 2 it 

 could not be doubted that the ,-, 1Qn ,-, . .. 



IG. 180. Encapsuled tape- worm embryo 

 TenebriO had devoured tape- (A\ and the resulting cystic worm, from 



worm eggs, whose enclosed em- Tenebrio 1nolitor ( x 10 )- ( After Stein -) 

 bryos had been liberated by the digestion of the egg-shell, and had 

 wandered through the intestinal wall into the body-cavity, where 

 they had lost their hooks, become encapsuled, and produced the tape- 

 worm head. 



Before the publication of these researches our knowledge of the 

 development of the tape- worms had been further increased by 

 Kiichenmeister's proof that the bladder-worm of the rabbit (Cysti- 

 cercus pisiformis) became a tape- worm (Tcenia) in the intestine of 

 the dog. 3 



The interest excited by this report was all the more intense since 

 it was the first instance of a " feeding " experiment. This result 

 had been attained by experiment, and it was speedily corroborated 



1 " Ueber den Generation swechsel der Cestoden ;" Zeitschr. f. wiss. Zool., Bd. ii., p. 

 210, 1850. " Beitrage zur Entwickelungsgesch. d. Eingeweidewiirmer, " ibid., Bd. iv. p. 

 205, 1852. 



2 Probably these were the larvae of a Tcenia occurring in its adult form in the mouse 

 (Tcenia inurina). 



3 Gtinsburg's Zeitschr. f. klin. Vortrage, p. 240, 1851. 



