IXTRODUCTIOX. 
Of the tapeworms parasitic in man there is one genus which is 
commonly overlooked in medical text-books, or at most passed over 
with only the slightest mention, namely, Hymenolepis. This genus, 
composed of a considerable number of species, is mostly restricted in 
its hosts to insectivorous mammals and birds, but three species, Hymen- 
olepis nana^ II clirninuta^ and H. lanceolata have been also reported 
from man. The first of these, II. nana^ is the most common of the 
three, and the most important. Like the larger tapeworms it is fre- 
quently the cause of severe symptoms, and indeed has been alleged by 
some authors to be productive of more serious effects than the former. 
In Italy, particularly Sicily, it seems to be one of the commonest para- 
sites; some authors estimate that as many as 10 percent of the children 
of certain classes in that country are infested b}^ it. Its existence in the 
United States has been practically ignored on account of its apparent 
rarity, only 1 case until recentlv having been reported for this country. 
There is, however, some evidence to show that II nana is consider- 
ably more common in the United States than general!}" supposed. 
Owing to the small size of the tapeworm in question and the conse- 
quent necessity of depending for a diagnosis of its presence upon the 
discovery of its eggs in the feces, it seems very probable that it has 
been overlooked many times; and it is expected that as the microscope 
comes more generally into use as an aid in diagnosis of diseases, new 
cases of H. nana will come to light from time to time. Weight is 
given to these statements by the fact within the past year 11 new cases 
have been added to the single one formerly on record for the United 
States; namely, 1 in Texas by Dr. John T. Moore, 1 in South Caro- 
lina and 3 in Georgia by Dr. Ch. Warded Stiles, and 6 in the District 
of Columbia by members of this laboratory." 
In the light of these recent developments Ilymenolepis juma appears 
to merit more attention than it has hitherto received in this country, 
and Doctor Stiles has accordingly requested me to prepare a paper 
upon the genus Hymenoleph^ taking into consideration such species as 
are of interest in human medicine. A paper similar to the present 
also seemed desirable from another standpoint; most of the literature 
is not generally accessible, being scattered in various foreign journals 
and in several languages; although Blanchard in 1891 published in 
French an excellent paper on the genus, which contained a complete 
resume of the literature then extant, practically nothing has appeared 
10 
o For additional cases see footnote, p. 7. 
