BOTHTtlOOEPHALUS. 129 



rather, its immature t^nioid condition is a frequent inhabitant 

 of fresh-water sticklebacks (Gasterosteus aculeatus, and G. pun- 

 gitus), hemg also found in the salmon and in the common salt-water 

 bull-head, or father-lasher {Gottus scorpio). The small sexually 

 immature tapeworm was formerly considered a separate species, 

 and was known under the title of Bothriocephalus soUdus. Some 

 years back CrepHn discovered the connection subsisting between 

 the two forms, and re-described the species in its two conditions 

 under the name of ScMstocephalus dimorphus ; but it was reserved 

 for Yon Siebold to explain the full nature of this relationship. In 

 his weU-known essay on the " Tape and Cystic "Worms," he shows 

 that it is not until the worm reaches the intestine of the ultimate 

 host that its segments acquire sexual completeness ; and this is a 

 law — as I have before had occasion to remark — which pervades 

 all classes of parasites. As Von Siebold observes, " the extent of 

 development in each individual will be found to be in proportion to 

 the time the parasite has passed in the bird's ahmentary canal after 

 its passive immigration."* A similar instance, it is added, "occurs in 

 the case of the Ligula simplicissima, infesting the abdominal cavity 

 of various species of carp, whose sexual organs are, and remain, 

 undeveloped, as long as the worm resides within the fish ; whilst, 

 when the latter is eaten by ducks, divers, waders, and other water- 

 fowl, the entozoon being thus conveyed into their intestines, it 

 attains perfect sexual development. In the older helminthological 

 works the sexually mature Ligula simplicissima is described under 

 various specific names, sometimes as Ligula sparsa, or L. uniserialis, 

 at other times as L. alternans, or L. interrupta." There can be little 

 doubt that many other so-called species of tapeworm infesting fishes 

 will eventually turn out to be the juvenile forms of adult cestodes 

 equally well known to science. 



Genera. — Bothriocephalus, Rudolphi ; = Dibothrium, Diesing ; 

 = (in part) Tcenia, Linneus ; = Bhytelmvnthus, Zeder ; = Bhytis, 

 Zeder ; = ScMstocephalus, Creplin ; Tetrabothrium, Rudolphi ; = 



* Band und Blasenwiirmer, s. 41. See also Huxley's translation, p. 32. 



