12 
Althouoli 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 only 
argimient. and moreover of little weight, since it is questionable 
whether such a division oilers any advantages, even when viewed from 
a purely practical standpoint. While the character selected by Cohn 
as a distinguishing mark is certain!}' an easy one to use (though the 
loss of hooks from the rostellum might in some cases proA’e mislead- 
ing), it does not seem to me that anything is to be gained by the sepa- 
ration of the various species now comprising the genus into the purely 
artificial groups proposed by Cohn, when it is almost certain that a 
revision will sooner or later be necessary, which will break up the 
genus along altogether ditferent lines. 
As there seems to be no sufiicient 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 
beyond the purposes of the present paper, if indeed such a revision 
could successfully be carried out at the present time, the three forms 
to be discussed will be regarded simply as belonging to the same • 
genus. Ilymenolejjis. and the dift'erences between them as of specific 
value only. 
KEY FOR THE DETERMIXATIOX OF THE SPECIES OF HYMEyOLEPI^ PARASITIC IX MAX. 
Strobila small, 5 to 45 mm. long, by 0.5 to 0.9 mm. Avide, filiform; head armed Avith 
a croAA'n of 20 to 30 hooks; eggs generally oA'al, A\fith filaments attached to the 
poles of the inner membrane; common Hymenolepis nana. 
Strobila 10 to 60 mm. long by 2.5 to 4 mm. AA ide; head unarmed; eggs generally round, 
prominent intermediate layer of albuminous substance betA\'een outer and inner 
membranes, outer membrane frequently Avith radial striations; rare 
Hymenolepis diminnta. 
Strobila lanceolate, 30 to 130 mm. long by 5 to 18 mm. broad; head small, compared 
A\ ith strobila, armed AA'ith 8 to 10 hooks; eggs OA'al, AA ithout filaments on the inner 
membrane; A-ery rare Hymenolepis lanceolata. i 
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 AA-ell deA'eloped, freely moA’able, 
armed A\fith a single croAA ii of 20 to 30 hooks, 14 to 18 p in length; suckers globular, 
80 to 150 p in diameter. Xeck long. Anterior segments A'ery 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 eA’en slightly exceed J 
« Synonyms. — Teenia murina Dujardin, 1845 (not T. murina Gmelin, 1790=CysO'ccr- 
cus fasciolaris Rudolph!) ; Teenia nana Siebold, 1852 (not Van Beneden, 1858); T. 
segyptiaca Bilharz, 1852 (not Krabbe, 1869); Diplacanthus nanus (Siebold) Weinland, 
1858; T. {Hymenolepis) nana Siebold of Leuckart, 1863; T. “rana’' of Bell, 1886 
(misprint); Hymenolepis nana B] 3 .nchRi'(\,lS 91 ; H //utrhirt Blanchard, 1891; ‘^Hyme- 
nolepsis’^ nana of Osier, 1895, and other authors (misprint); Tecnia ‘■'minima'^ of * 
Huber, 1896 (misprint for T. murina). 
