PARASITES 



363 



llnishcd handling mice Icsl his hands may have become contaminated with 

 the eggs which might be transferred to the mouth. 



Hymenolepis diminuta (rudolphi, 1819). — This (Figs. 143B, 145 and 

 146) is one of the most common tapeworms of the mouse and rat, and it 

 sometimes occurs in man. It is also cosmopolitan in its distribution, having 

 been reported from various places in the United States, Europe, and South 

 America. Bacigalupo (2) reports that 28 per 

 cent of 300 rats from Buenos Aires were infected. 



Stiles and Crane (37) give the following 

 complete description of the species: "Strobila 

 10 to 60 millimeters in length, 2.5 to 4 

 millimeters in maximum breadth; composed of 

 800 to 1300 segments. Head small, almost 

 globular; 200 to 600 /jl in width; rostellum 

 rudimentary, pyriform, only slightly protractile; 

 hooks absent; suckers globular, near the apical 

 portion of the head, 80 to 160 fx in diameter. 

 Neck usually short. Segments throughout 

 strobila broader than long. Genital pores on left 

 margin, near the junction of the anterior and 

 middle thirds of each segment. Three testes in 

 each segment; vas deferens dilates into a 

 prominent seminal vesicle before entering the 

 cirrus pouch, within which also is a vesicle. 

 Gravid uterus occupies most of the proglottids ; 

 its cavity is subdivided into a large number of 

 incompletely separated compartments tilled 

 with eggs. Eggs round or slightly oval; outer 

 membrane 54 to 86 jj, in diameter, yellowish in 

 color, may be radially striated; inner membrane 

 24 by 20 /i to 40 by 35 )U in diameter, with mammilate projection at each 

 pole often not apparent; between outer and inner membranes a prominent 

 third layer of albuminous substance, often appearing as two delicate smooth 

 membranes, with intervening space filled by a granular coagulum; embryonal 

 hooks II to 16 /i in length." 



The completion of the life cycle requires an intermediate host. This 

 may be one of quite a number of insects, although probably the adult 

 Tenebrio niolitor and the rat fleas, Nosopsyllus fasciatus and Xenopsylla 

 cheopis, are the more natural intermediate hosts. 



Fig. 144. — Longitudinal 

 section of the intestinal villus 

 of a rat containing cystic 

 stage of Hymoiolcpis nana. 

 (Enlarged.) {From Stiles 

 and Crane, after Grassi and 

 Rovelli.) 



