12 
Although the plea of utility is an argument which might be advanced 
in favor of Cohn's division of the genus, it is, in fact, about the onl}" 
argument, and moreover of little weight, since it is questionable 
whether such a division offers any advantages, even when viewed from 
a purely practical standpoint. While the character selected by Cohn 
as a distinguishing mark is certainly an eas}^ one to use (though the 
loss of hooks from the rostellum might in some cases prove mislead- 
ing), it does not seem to me that anything is to be gained b}^the sepa- 
ration of the various species now comprising the genus into the purely 
artificial groups proposed bv Cohn, when it is almost certain that a 
revision will sooner or later be necessaiy, which will break up the 
genus along altogether different lines. 
As there seems to be no sufficient reason, either from theoretical 
or practical considerations, for recognizing' Cohn’s division into sub- 
genera, and as an attempt to revise the genus upon a rational basis is 
be}mnd the purposes of the present paper, if indeed such a revision 
could successful!}" be carried out at the present time, the three forms 
to be discussed will be regarded simply as belonging to the same 
genus, ILjmenolejns^ and the differences between them as of specific 
value only. 
KEY FOR THE DETERMINATION OF THE SPECIES OF HYMEXOLEPLS PARASITIC IN MAN. 
Strobila small, 5 to 45 mm. long, by 0.5 to 0.9 mm. wide, filiform; head armed with 
a crown of 20 to 30 hooks; eggs generally oval, with filaments attached to the 
poles of the inner membrane; common Hymenolepis nana. 
Strobila 10 to 60 mm. long by 2.5 to 4 mm. wide; head unarmed; eggs generally round, 
prominent intermediate layer of albuminous substance between outer and inner 
membranes, outer membrane frequently with radial striations; rare 1 
Hymenolepis diminuta. 
Strobila lanceolate, 30 to 130 mm. long by 5 to 18 mm. broad; head small, compared 
with strobila, armed with 8 to 10 hooks; eggs oval, without filaments on the inner 
membrane; very rare Hymenolepis lanceolaia. 
The Dwarf Tapeworm — HYMENOLEPIS NANA« ( Siebold, 1852) Blanchard, 
1891. 
Specific diagnosis. — Hymenolepis: Strobila 5 to 45 mm. in length, and 0.5 to 0.9 
mm. in maximum breadth, composed of, about 100 to 200 segments. Head sub- 
globular, 130 to 480 p in diameter; rostellum well developed, freely movable, 
armed with a single crown of 20 to 30 hooks, 14 to 18 p in length; suckers globular, 
80 to 150 p in diameter. Neck long. Anterior segments very short; following seg- 
ments 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 
« Synonyms. — murma Hujardin, 1845 (not T. murina Gmelin, 1790=Ci/shcer- 
cus fasciolar is Rudolphi); Teenia nana Siebold, 1852 (not Van Beneden, 1858); T. 
segyptiaca Bilharz, 1852 (notKrabbe, 1869); Diplacanthus nanus (Siebold) Weinland, 
1858; T. {Hymenolepis) nana. Siebold of Leuckart, 1863; T. “rana’^ of Bell, 1886 
(misprint); Hymenolepis nana Blanchard, 1891; H. murina Blanchard, 1891; Hymc- 
nolepsis^^ nana of Osier, 1895, and other authors (misprint); Teenia minima of 
Huber, 1896 (misprint for T. murina). 
