OEIGIN OF THE PKOGLOTTIDES. 



45 



lescent, being only denoted by imperfect transverse folds on the 

 sides of the body. Here, in fact, many groups of hermaphrodite 



Fig. 23. 



sexual apparatus become developed close together, in the ribbon- 

 like body of the full-grown agamozooid, but the parts which 

 surround them do not break up into joints. In this respect 

 we may compare a Ligula, as a compound animal, with certain 

 polypidoms in which the individuals become, in a similar manner, 

 less distinctly separate from the parent stock. 



For how long a time the head end of the cestoid worm can 

 play the part of an agamozooid, and how many sexual individuals 

 such a tape- worm can produce, has not yet been certainly proved. 

 The number of proglottides which a single scolex can bring forth, 



Fig. 23. Represents, diagrammatically the metamorphosis of a Tetrarhynchus into a 

 Rhynchobothrium (after Van Beneden, see also supra, fig. 19). A. A Tetrarhynchus 

 scolex, whose posterior extremity is growing and elongating. B. The elongated hinder 

 extremity exhibits transverse wrinkles which indicate the boundaries of the future 

 joints, c. The posterior end of the same scolex appears clearly jointed, i. e. provided 

 with proglottides. The Tetrarhynchus has thus become a Rhynchobottirium. a. One of 

 the four sucking disks, b. Protruded part of the four proboscides provided with 

 recurved hooks, c. Middle portion of the four proboscidean tubes, e. Unarticulated 

 portion of the body, e* Transversely wrinkled portion of the body, e** Articulated 

 part of the body giving rise to proglottides. 



