56 SANITARY ENTOMOLOGY 



species likely to be eaten by animals of the species that harbors the 

 adult tapeworm. 



Inasmuch as Nicoll and Minchin (1911) have found cysticercoids in 

 a rat flea (Ceratophyllus fasciatus) that in details of head structure are 

 apparently exactly similar to and specifically identical with the dwarf 

 tapeworm, the question arises whether such insects may not act as inter- 

 mediate hosts, and whether in addition to the life cycle of an exceptional 

 type described by Grassi, the dwarf tapeworm also has a life cycle of 

 the ordinary type. T. H. Johnston has found cysticercoids similar to 

 those recorded by Nicoll and Minchin in another species of rat flea 

 (Xenopsylla cheopis) as well as in Ceratophyllus fasciatus. 



Joyeux (1916) has failed in experiments with fleas belonging to the 

 species named and to related species, to infect them with H. nana. He 

 states he used both larval and adult fleas. On the other hand he was able 

 to confirm Grassi's results and succeeded in infecting a large number of 

 rats and mice by feeding them the eggs of the tapeworm. The experi- 

 mental evidence thus far available accordingly favors the view that insects 

 do not play a necessary part in the life history of the dwarf tapeworm. 

 Furthermore, considering the frequency of occurrence of H. nana as 

 a parasite of man, and the enormous numbers of the parasites sometimes 

 present, it would seem that infection is more likely to occur in the manner 

 described by Grassi than as a result of swallowing rat fleas, there being 

 of course a greater likelihood of human beings swallowing rat feces or 

 fecal matter from other human beings containing large numbers of eggs 

 of the tapeworm than of swallowing rat fleas containing a sufficient num- 

 ber of cysticercoids to develop into the large number of tapeworms that 

 have been found in some cases. 



Choanotcenia infundibulum (Bloch, 1779) Cohn, 1899 



Choanotcenia mfumdibulum is a common tapeworm of chickens in 

 various parts of the world. Grassi and Rovelli (1892) in Italy found 

 cysticercoids in the common house fly (Musca domestica) which on 

 account of their morphological similarity to Choanotcenia vrtfundihulum 

 they inferred belonged to this species. From the results of experiments 

 conducted in this country by Guberlet (1916) it appears safe to conclude 

 that the common house fly acts as the intermediate host of the tapeworm, 

 Choanotcenia imfundihulum, infection of the fly apparently occurring as 

 a result of swallowing the eggs of the tapeworm, and the chicken in turn 

 acquiring the parasite as a result of swallowing flies infested with the 

 cysticercoid stage. Whether infection of the fly reg ilarly occurs during 

 the larval or during the adult stage, or during both stages, has not been 

 definitely settled. 



