230 ORGANISMS ILLUSTRATING BIOLOGICAL PRINCIPLES 



tract of the host, producing a string of as many as 3000 to 4000 seg- 

 ments or proglottids, often reaching a length of ten meters. Mature 

 proglottids, passed from the host with the feces, must reach water, 

 where the eggs are shed. After a developmental period in the water, 

 the eggs hatch into free-swimming larvae (coracidia), which to continue 

 development must be eaten by a copepod. The parasites penetrate 

 the intestinal wall and so reach the body cavity of this host, where 

 they develop until the copepod is in turn eaten by a fish, when they 

 usually penetrate to the flesh of the host and grow to approximately 

 six millimeters in length. Various fishes, such as the northern pike, 

 Esox lucius, wall-eyed pike, Stizostedion vitreum, sand pike, S. cana- 

 dense griseum, as well as the burbot, Lota maculosa, may all serve 

 as second intermediate hosts for this important parasite. Man and 

 other carnivores acquire the infection by eating improperly cooked 

 fish. 



The bass tapeworm which matures in large- and small-mouthed 

 black bass also requires three hosts — copepods, small fishes which 

 carry the larval stage encysted in the viscera, and the final host, or 

 adult bass. The life cycle of this parasite illustrates very clearly 

 the interdependence of organisms necessary for the completion of the 



Adult yellow grub, enlarged 

 from mouth cavity of hejxn« 



•i>;^@ e-Maturtegg ^o^' — "— "^^--tS 



N. Y. State Conservation Dept. 



Diagram of the life cycle of the yellow grub of bass (C. marginatum). (1) The 

 adult fluke in buccal cavity. (2-4) Embryo within egg hatches as free living 

 miracidium which, upon entering snail, produces a mother sporocyst and two 

 generations of rediae (5-8), cercariae (8-9), liberated by the daughter redia, 

 penetrate many species of fish (10-11) and mature when eaten by various 

 herons (12). 



