334 THE DEVELOPMENT OF CESTODES. 



appear in the development of the cystic worm from the egg is the 

 caudal bladder." The so-called head rises subsequently, " invaginated" 

 in the interior of the bladder, " like a candle within a lantern." We 

 have to thank G. Wagener * for having called attention to these for- 

 gotten researches, and for having confirmed them by observations of 

 his own. 



Even v. Siebold found himself compelled to abandon the idea that 

 the formation of the bladder was a secondary and abnormal process. 

 This was due much less to Kuchenmeister's polemic 2 against the 

 theory of degenerate and strayed worms than to the above observa- 

 tions on the encysted tape -worms of Tenebrio, whose resemblance 

 to the bladder -worms was so great that even Stein declared the 

 Cysticerci to be nothing else than the second post-embryonic stage 

 of certain Tcenice. Correct as this statement was, Stein could not 

 perfectly escape the influence of Siebold's theory. He did not venture 

 fully to identify the bladder- worms with the encysted tape- worms, 

 but noted the following distinction between them " that the former 

 seemed to be pathologically degenerated by the accumulation of a 

 dropsical fluid in the hinder part of the body, and would possibly 

 never be able to become mature tape-worms." 



This is, indeed, the opinion which is maintained by v. Siebold in 

 his later work on tape-worms and bladder- worms, 3 and which, sup- 

 ported by the authority of a famous name, has still been held by 

 many even within the last few years. 



The morphological identity between the Cysticerci and the " second 

 developmental stage" of the Cestodes had been asserted by van 

 Beneden* even before Stein. It was, it is true, in connection, not 

 with Tcenice, but with marine tape- worms the Tetrarhynclii that 

 the former had studied this second stage, but that does not in any 

 way affect the importance of his statement. On the contrary, he 

 thereby further proved that the cystic stage was in nowise confined 

 to the Tcenice, but had a wide, perhaps general, distribution among 

 the Cestodes. 



But not only did van Beneden prove the existence of a cysticercoid 

 stage in the Tetrarhynchi ; he also called attention to this fact, that 

 the cysticercoid Tetrarhynchus (Anthocephalus) was found especially 

 in the bony fish, and that they afterwards passed over to the rays 

 and sharks, in which the adult Tetrarhynchus (Rkynchobothrius) was 



1 "Enthelininthica.," Dissert, inaug. Berol., p. 30, 1843. 



2 "Die Cestoden im Allgemeinen, " Prager Vierteljahrsschr., loc. cit., p. 9 et seq., 1853. 

 s " Ueber die Band- und Blasenwiirmer nebst einer Eiuleiturig liber die Entstehung 



der Eingeweidewurmer,*' p. 60, 1854. 

 * -'Lea vers Cestoides," p. 83, 1850. 



