30 ANIMAL PARASITES. 



Von SiebokPs views_, just as Von Siebold himself has done re- 

 peatedly. In the fourth volume of his ' Zeitschrift/ p. 407, the 

 latter let fall the expression, " cystic worms are diseased drop- 

 sical tape-worms," but only in order to maintain the more firmly 

 that they are degenerated tape- worm larvae, and he also persevered 

 in the same course in his memoir, ' Ueber Bund- und Blasen- 

 wu'rmer/ 1854, p. 64, in which he at the same time throws 

 together nearly all the large-hooked tape-worms of man, the dog, 

 the fox, and the marten, and regards them as different races of a 

 single species. 



After the greater part of the zoologists of Germany and 

 other countries, with the exception of Von Siebold, Diesing 

 (' Ber. der Wiener Acad./ 1853, p. 421), Valenciennes (' Comptes 

 rendus/ 1855, xl, p. 1000), and, amongst others, even the Com- 

 mission for the examination of the Danish prize essay (Eschricht, 

 Steenstrup, and Hannover), had acceded to my views; R. 

 Leuckart especially, in his most recent work, confirmed all that 

 I had said on the production and nature of the cystic worms, 

 as well as on the metamorphosis of the T&nice. Leuckart 

 recalls his previous statements, and shows that Von Siebold 

 differed from me only in words, but not in any real dif- 

 ference of opinion and facts ; that Von Siebold's views had 

 become essentially different in the course of the year, and, as 

 Von Siebold said, not a little modified, as he supposes that 

 the cystic worms are of an embryonic nature, that their caudal 

 vesicle is founded in the plan of development of the cestoid 

 worms, and not produced by a pathological process. In short, 

 Leuckart agrees essentially with all my statements and 

 views. 



But to place it beyond all doubt that the cystic worms were 

 necessary steps in the development of the Teenies, it was also 

 requisite to prove their production from the embryos of the 

 tapeworm-brood. It is true that the six characteristic embryonal 

 booklets have not yet been detected upon true vesicular worms, 

 but we shall shortly see that the laws of analogy, as well as 

 experiment, afford us a glance into this process. Thus Stein 

 (Siebold and Kolliker's ' Zeitschr./ iv, p. 203) saw the embryos 

 of a species of tape-worm, after their transfer to the intestine 

 of an animal (the mealworm-beetle), break out of their egg- 

 shells, penetrate the walls of the intestine, become encysted, as 

 he erroneously says, with the loss of their six booklets, outside 



