RELATION OF INSECTS TO THE PARASITIC WORMS 55 



adult moth by Grassi and Rovelli were carried over from the larval stage 

 of the insect. He failed in his attempts to infect Forficula auricidaria, 

 Blatta orientaUs, and Blattella germanica. He also failed to infect 

 beetles belonging to the species Blaps viortisaga, but succeeded easily in 

 infecting the adults of Ten'ebrio molitor. The larvae of this latter beetle 

 according to Jo^^eux are incapable of acting as intermediate hosts of 

 H. diminuta. He was able to infect the larva? of rat fleas and of Pulex 

 irritans and Cfenocephalus canis. In these insects the embr3'os of //. 

 dinmiuta begin immediately to develop into cysticercoids and do not wait 

 for the transformation of the larval fleas into adults, as Joyeux found in 

 the case of Dipylidium caninum, the embryos of which apparently lie 

 dormant in the insect until after it transforms into the adult stage. In 

 this country Nickerson (1911) has reared the cysticercoid in myriapods, 

 Fonfaria virginiensis and Jidus sp., fed on the eggs of the tapeworm. He 

 failed in his attempts to infect meal worms. 



It is evident that infection of the definitive host with H. diminuta 

 results from swallowing infested insects, the latter having become infested 

 as a result of swallowing the eggs contained in the feces of animals harbor- 

 ing the tapeworms. As a parasite of man in the United States, so far as 

 available statistics show, H. diminuta ranks about third in frequency 

 among the tapeworms, the beef tapeworm (Tcenia saginata) being the 

 most common, and the dwarf tapeworm (H. nana) being next. Evident 

 prophylactic measures are those directed toward the destruction of rats 

 and mice and the avoidance of the ingestion by human beings of the 

 various insects that may serve as intermediate hosts, especially the pro- 

 tection of farinaceous foods from insect infestation. 



Hymenolepis nana (Siebold, 1852) Blanchard, 1891 



Hymenolepis nana (the dwarf tapeworm) is a very common intestinal 

 parasite of rats and mice and is of rather frequent occurrence in man, 

 especially in children. In the United States it ranks second to the beef 

 tapeworm in the order of frequency among the tapeworms of man. Its 

 life history has not been fully worked out. Grassi (1887), however, has 

 found that cysticercoids develop in the intestinal villi of rats that have 

 been fed the eggs of the dwarf tapeworm. According to his view the 

 cysticercoids later break out of the villi into the lumen of the intes- 

 tine and grow into mature tapeworms. The rat thus acts both as inter- 

 mediate and definitive host of the dwarf tapeworm, the parasite being 

 spread from one rat to another through the medium of the eggs passed 

 in the feces. Tlie dwarf tapeworm, according to Grassi's version of the 

 life cycle, is an exception to the rule among tapeworms that the adult 

 stage occurs in one species of animal and the larval stage in another 



