744 DESCRIPTION OF BOTHRIOCEPHALUS CORDATUS. 



varied from 125 to 154. The only differences associated with the 

 growth of the joints and head (measuring over a millimetre) lay in the 

 beginning of sexual development. Even in those 80 mm. in length 

 I could recognise in the larger middle joints a generative aperture 

 and cirrhus-pouch, and in the .interior, in soaked specimens, the 

 rudiments of the ducts, while in specimens 100 mm. long the genera- 

 tive apparatus could be seen in greater completeness and distinctness. 

 The median region had at the same time swollen out into a longitudinal 

 elevation, as in adult forms, evidently an indication of further sexual 

 development. Curiously enough, it was the median segments of the 

 body which were best developed, not only in size (1'2 mm. long), 

 but in the structure of the generative organs ; only in larger forms 

 did this distinction disappear. In a specimen 27 cm. in length, 

 with 184 proglottides, which had already liberated some of its 

 posterior proglottides, all the joints except the anterior 40 to 60 

 were quite mature. 



I thought at first that the above peculiarity was confined to this 

 species of Bothriocephalus. Since then, however, we have learned, 

 from the researches of Kahane 1 and Eiehm 2 , that in Tcenice also the 

 last joints of the chain are very often sterile and small, and that the 

 sexual development always begins at some distance from the oldest 

 joint. The number of these barren joints varies very considerably ; 

 though generally but few, they include in some species about half of 

 the whole chain, and thus give the young worms a form strikingly 

 different from that of the adults. In the case of Tccnia perfoliata 

 from the horse, the young form has, as Kahane has shown, been even 

 regarded as a distinct species (T. plicata). The case of B. cordatus is 

 probably similar ; the last joints of the young chain probably remain 

 sterile, and separate without further growth or development. B. latus 

 seems, according to Braun's report, to be different in this respect, so that 

 the present species probably exhibits also this difference in development, 

 though it can hardly be supposed that it stands alone in this respect. 

 In fact B. proboscideus from the salmon exhibits young forms with 

 6 to 16 joints, which when 1'9 to 4 mm. in length, exhibit the same 

 form and posterior structure as those of B. cordatus. The segmenta- 

 tion begins close behind the head, which has of course at first, as in 

 all Bothriocephali, a much smaller size than it subsequently acquires 

 with the development of its adult structure. 



That it is from fish that the dog and man are infected with 

 Bothriocephalus cordatus, can, from the analogy of B. latus, hardly 



1 Kahane, " Anatomic von Tsenia perfoliata." Zeitschr. /. Wins. Zod., Bd. xxxiv., 

 p. 184. 



3 "Studien an Cestoden," p. 56 : Halle, 1881. 



