DEVELOPMENT OF SCOLICES. 



37 



integument. In the substance of their bodies, spherical or 

 discoidal bodies of a glassy appearance are often seen : these 



Fig. 19. 



have frequently been mistaken for eggs, whereby the nature of 

 these creatures has been wholly misconceived. The particles are, 

 in fact, nothing more than organized deposits of carbonate of 

 lime. Integumentary concretions of the same kind are found in 

 many other of the lower animals. The scolices have also been 

 described as young cestoid worms : we shall, however, more 

 readily comprehend the various stages through which the Ces- 



Fig. 19. Series of developmental stages of a Tetrarhynchus, or rather of a scolex of 

 Rhynchobothrium, represented diagrammatically, and partly after Van Beneden. The 

 cestoid embryo becomes a receptaculum scolicis by the development of a scolex in its 

 interior. With the progressive development of the scolex the body of the embryo 

 (receptaculum scolicis') and the cyst containing it, increase in dimensions. 1. The 

 encysted embryo. 2. The encysted embryo developes a bud internally, and so becomes 

 the receptacle of a scolex. 3. The internal bud out of which a scolex is being developed 

 has increased in size. 4. In the interior of the bud the head of the future Tetrarhynchus 

 appears, and the stickers become perceptible. 5. The head of the Tetrarhynchus 

 becomes more clearly denned ; and, 6, acquires a neck. 7. The neck elongates, the four 

 hooked proboscides make their appearance. 8. The more elongated neck is forced to 

 become curved in order to accommodate itself to the narrow space in which the scolex 

 is undergoing its development. 9. The adult scolex out of its cyst, and beginning to be 

 extruded from its receptacle. 10. The extruded scolex; which, in 11, has separated 

 itself from its receptaculum. In this condition, the scolices of the Rhynchobothria 

 have hitherto been described as species of Tetrarhynchus. * Scolex. ** Receptaculum 

 scolicis. *** Cyst. For the further development of the Tetrarhynchus into a Rhyncho- 

 bothrium, see fig. 23. 



