PLATE XIT. 



The figures i to 5 are intended to show semi-diagrammatically the 

 different stages of the metamorphosis or the ' alternation of genera- 

 tions' in the life of one of the typical Taenioid Flatvvorms or Platy- 

 elminthes. Figure i represents the perfect animal as it is found 

 in the compound form, called ' strobile/ from the analogy of the 

 cone of a fir, in the intestinal canal of ordinarily a carnivorous or 

 omnivorous vertebrate ' host/ such as the dog, or the human sub- 

 ject. Figure 2 represents one of its segments, the so-called ' pro- 

 glottides/ as it may be seen before the great development of the 

 ova in the uterus has overwhelmed and caused the disappearance 

 of the other sexual organs, female and male, which each segment 

 after the sexless adherent Miead' or ^ nurse' contains. Figures 3 

 and 4 represent ripe segments of the compound animal, so dis- 

 tended with ova as to have caused the ripe proglottides, which 

 retain considerable locomotor powers, to be called ' ovaria ambu- 

 lantia.' Figure 5 shows one of the microscopic embryos, the 

 so-called 'proscolex,' as it appears when set free from its shell by 

 the action of the digestive secretions of the intestinal tract, into 

 which it is introduced ; the entire ovum having been set free from 

 the substance of the ' proglottis' by its spontaneous or other dehis- 

 cence, inside or outside of the digestive tract of the animal, which 

 is to be its. host. Figure 6 shows the cystic stage into which such 

 a proscolex as that shown in Figure 5 developes into, when it has 

 belonged to Taenia caenurus, which differs from other Tapeworms 

 except Taenia echinococcus, in having its proscolex proliferating as 

 shown in the figure, instead of producing a solitary ' new head' or 

 ' scolex.' This cystic stage is passed in the parenchyma of some 

 solid organ, such as the liver or the muscles ; and in the particular 



