160 Phylum Plat helminthes 



Bibliography 



Jahn, T. L., and Kuhn, L. R. 1932. The life history of Epibdella melleni Mac- 



Callum 1927, a monogenetic trematode parasitic on marine fishes. Biol. Bull. 



62:89. 

 Nigrelli, R. F. 1932. The life-history and control of a destructive fish parasite 



at the New York Aquarium. Bull. N. Y. Zool. Soc. 34:123. 

 Nigrelli, R. F., and Breder, C. M., Jr. 1934- The susceptibility and immunity of 



certain fishes to Epibdella melleni, a monogenetic trematode. /. Parasit. 20:259. 



Class Cestoidea 



INTERMEDIATE STAGES OF CESTODES 



Reed O. Christenson, University of Minnesota 



THE most available cestode for general laboratory use is Taenia 

 pisiformis which occurs in the body cavity, about the mesenteries, 

 or in the liver of native rabbits as a cysticercus, and comes to maturity 

 in the intestinal tract of dogs and related carnivores. By autopsy of a 

 dozen or so cottontail rabbits, ample material may usually be obtained 

 to establish a permanent laboratory supply. 



The parasites, in the infective larval stage, appear as small (pea- 

 sized) vesicles enclosing a head and encased in an adventitious con- 

 nective tissue capsule. Occasionally worm-like motile stages are found 

 free in the body cavity, or the parasites may be seen as regular white 

 blotches in the liver. These are developmental stages and are not suit- 

 able for infection. 



Encapsulated cysts are fed with meat to tapeworm-free dogs. In 

 about 5 or 6 weeks an examination of the feces will disclose the terminal 

 segments discharged from the worms. These contain ova composed of 

 the hexacanth embryos covered by the striated embryophore as char- 

 acteristic of the true taeniae. The ova are easily demonstrated by 

 macerating a segment in water, mounting a drop on a slide, covering and 

 studying microscopically. To infect rabbits, the ova are added to a moist 

 bran mash and fed directly to young animals. 



When the ova enter the alimentary canal the hexacanths free them- 

 selves of their covering, penetrate the host tissues to the blood stream, 

 and are carried to the liver. Here they migrate about in the tissues 

 for a while and by the 24th day have come to the surface where they 

 appear as regularly contoured white blotches. They migrate again, 

 leaving the liver, and come to lie free in the peritoneal cavity as elongate, 

 worm-like bodies. These ultimately assume a spherical shape and be- 

 come encapsulated, thus reaching the infective stage. 



The behavior of the cysticercus upon liberation is of some interest. 

 They may be studied by teasing away the connective tissue capsules, care 



