PISCES 469 



gulls, and divers), but in the young or sexually-immature 

 taenioid condition it is a frequent inhabitant of sticklebacks 

 (Gastereosteus aculeatus and G. pungitus), being also found in 

 the salmon and in the bull-head, or father-lasher (Coitus 

 scorpio). The immature tapeworm was formerly considered a 

 separate species (B. solidus). Some years back Creplin dis- 

 covered the connection subsisting between the two forms, and 

 re-described the species in its two conditions under the name 

 of Schistocephalus dimorphus, but it was reserved for Von 

 Siebold to explain the full nature of this relationship. In his 

 essay on " 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. As Yon 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 alimentary 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 intestine, it 

 attains perfect sexual development. In the older helmintho- 

 logical works the sexually- mature Ligula simplicissima is 

 described under various specific names (L. sparsa, L. uniserialis, 

 L. alternans, L. interrupta) ." These results have been con- 

 firmed by later observers, but it is now usual to recognise the 

 sexually-mature worm as the Ligula monogramma of Creplin. 

 In 1876 Dr Duchamp published his beautiful memoir on this 

 subject, treating the entire question exhaustively and adding 

 important experimental details. M. Duchamp gives a list of 

 about twenty species of fish that are infested by the immature 

 worm, and amongst these the Cyprinidce play by far the most 

 conspicuous part. M. Duchamp has recorded a fatal piscine 

 epizooty amongst tenches (Tinea vulgaris), occurring in the 

 ponds of La Bresse. This is produced by Ligula simplicissima, 

 which escapes by an aperture formed near the vent of the 

 infested fish. M. Duchamp also gives important anatomical 

 and embryological details, but the especially interesting part 

 of his memoir refers to his feeding experiments, seven in 

 number. He succeeded in rearing L. monogramma in the 

 domestic duck, by feeding this bird with examples of L. simpli- 



