350 



from the class of worms, and tha 

 applies as well to the lowest 



■I 



The Turbellaria then, so fa; 



velop (a) by fission! (M from - 



through the following stages, 

 however, all observed in a si 



3. A quiet, encysted (?) stage (Girard's Planocera). 



4. Articulated stage observed in one species (Agassiz's Plo- 

 naria angulata). 



5. Adult, ciliated, not segmented. 



Development of the Trematodes. The flukes are parasitic 

 worms, with a sucking disk in the centre of the body by which 

 they attach themselves on or within the body of their host. The 

 fluke or "liver worm" (Distoma hepaticum) lives in the liver of 

 the sheep and of man. The fishes and snails are much infested 

 by them, nearly each species having its distinct kind of tluke. 

 The adult flukes are not ciliated, the alimentary canal ends in « 



For the mode of formation of the egg of the Trematodes. and 

 the embryonic history of certain forms, the student is referred to 

 Leuckart's " Menschlichen Farasiten" and E. Van Beneden's 

 beautiful "Researches." E. Van Beneden has shown that the 

 development of the Trematodes begins by subdivision of the 

 g< rminative cellule or nucleus. The nucleus and nucleolus then 

 divide and subsequently the "protoplasmic body." The yolk, 

 however, remains entirely independent of this division, and sem s 

 as nourishment for the other cells forming the body of the 



From Van Beneden's observations, it appears that the eggs of 

 the lower flukes as a rule undergo total segmentation, and the 

 young are hatched either oval, ciliated, Infusorian-like, without 

 anv organs, not even eye-specks, as in Distoma and Araphistoma ; 

 or "as in the highe, 



