PLATYHELMINTHES CESTODA 



and with those of the head. Each joint contains at first male 

 genitalia comparable with those of a Trematode ; then the female 

 organs develop, and finally self- fertilisation follows. The Cestodes 

 feed through their skin, probably by the aid of fine protoplasmic 

 processes, which penetrate the tough investing membrane and 

 absorb the already digested food which bathes them. When a 

 proglottis of Calliobothrium is approaching maturity it separates 

 from the parent, the broken ends of muscles, nerves, and excre- 

 tory vessels speedily heal, and it is now cap- 

 able of continued growth and of fairly active 

 movement if it remains in the intestine of 

 the host. According to van Beneden, it may 

 even attain a size equal to, or exceeding, that 

 of the whole parent or " strobila." * These 

 considerations led Leuckart, von Siebold, P. J. 

 van Beneden, and others, to Steenstrup's con- 

 clusion that a jointed tape-worm is really a 

 colony composed of two generations the 

 head and neck derived from the larva, and 

 the proglottides produced by the segmenta- 

 tion of the neck. 2 This view of the colonial 

 nature of jointed Cestodes was generally 

 37. Archigetes adopted from 1851 to 1880. During the 



t/i7//4* //Y*k*uwMs7*'_ * 



last fifteen years, however, the varied inter- 

 pretations of the facts of the ontogeny of this 

 app, Persistent larvai group have led some authors to adopt the 

 tl^porf- 'M' 86 Dionozootic view (that a Cestode is one indi- 

 sistent larval hooks ; vidual), others are still of the older opinion, 



FIQ. 



sieboldii (appendi- 



cuiatus), from the 



testeT- and Hatschek (Lelirbuch, p. 349) and Lang 

 yg, yolk-glands, take up intermediate positions. Lang considers 

 art) that the formation of the joints of a tape- 

 worm from a small fixed " scolex," is not only largely comparable 

 with the strobilation of a scyphistoma and the consequent forma- 

 tion of a pile of medusae, as in the life-history of Aurelia, but 



1 The mature proglottis of Calliobothrium eschrichti is 8-9 ram. long, whereas 

 the strobila only measures 4-5 mm. in length. Species of Phylliobothrium, Antho- 

 bothrium, and Tetrarhynchus show a similar but not an equal contrast between 

 the size of the parent and proglottis (P. J. van Beneden, "Les Vers Cestoides," 

 Nouv. M&m. de I'Acad. Roy. d. Bclgique, torn. xxv. 1850). 



2 The difficult question of the nature of the Cestode body and Cestode larvae 

 is adequately discussed by Braun, loc. tit. p. 1167. 



