52 
increase in length and breadth, but remain broader than long, except that the length 
of the hindermost segments may occasionally equal or even slightly exceed their 
breadth. Genital pores on the left margin, near anterior border of each segment. 
Three testes in each segment; vas deferens enlarged to form a seminal vesicle within 
the cirrus pouch, while a seminal reservoir outside the cirrus pouch is only slightly 
developed or absent. Gravid uterus occupies nearly the entire segment; wall of 
uterus with a few inconspicuous infoldings, forming incomplete partitions extending 
Fig. 81. — Head and strobila of dwarf tapeworm ( Hymenolepis nana). Enlarged. (After Leuckart, 
1863, 393, fig. 112.) 
Fig. 82. — Head of dwarf tapeworm ( II. nana) . Enlarged. (After Leuckart, 1863, 394, p. 113.) 
Fig. 83. — Hooks of Hymenolepis nana: a, complete crown; b, isolated hooks. Enlarged. (After 
Frantz, from Kuechenmeister & Zuern, 1881a, pi. 5, fig. 4.) 
into the cavity of the uterus. Eggs number 80 to 180 in each segment; oval or 
globular; two distinct membranes; outer membrane 30 to 60/* in diameter; inner 
membrane 16 to 34/* in diameter, presenting at each pole a more or less conspicuous 
mammillate projection, provided with filamentous appendages; embryonal hooks 10 
to 14/* long. 
Habitat. « — Small intestine of brown or Norway rat (J lus decumanus ), black rat 
(Mus rattus ), dwarf field mouse ( Mus minutus ), house mouse ( Mus musculus), garden 
dormouse ( Eliomys quercinus) , and man ( Homo sapiens). 
a There is- some slight doubt as yet as to the absolute identity of the parasite in 
man with that of rodents, but from a standpoint of prevention they should at present 
be considered identical. The form in the rat (type host Mas decumanus, in France) 
may at least be viewed as a host subspecies (II. nana fraterna Stiles, 1906). 
