18 
0.15 mm. to 0.17 mm. long, from 0.8 to 0.9 mm. broad; all the segments having 
their posterior angles somewhat salient, sharp, shaped like saw teeth; genital 
orifices unilateral; testicle [misinterpretation of seminal receptacle] claAnform, ex- 
tending transversely from the middle to the receptacle of the penis in the shape of 
a retort; penis smooth, very slender, not very salient; eggs elliptical with three 
envelopes; the external one 0.065 mm. long; the middle one membranous, in folds, 
0.05 mm. long; the internal one more resistant, somewhat oblong and terminating in 
an obtuse point at each extremity; embryo from 0.029 mm. to 0.030 mm. long, with 
hooks from 0.015 mm. to 0.016 mm. long. 
I found it at Rennes in a brown rat {Mus deciimamis,) , in a dwarf field mouse {Mus 
pdmilus) [=J/. minutus'], and in a garden dormouse {^[yox'as nitela) \^=Eliomys 
quercinus ] . ( Translation. ) 
Blanchard (1891a). Moniez (1888), and Linstow (1896a) inclined to 
the opinion that the two forms 'Tsenia nana and Tsenia mwnna are 
distinct species. Blanchard (1896b). however, has more recent]}^ come 
to the conclusion that the slight inconstant differences which have been 
noted in the two forms are sufficiently accounted for by the difference 
in habitat, and that the two worms should be united under one species, 
which he would for reasons of priority call Hymenolepis murina. But 
since the name Tsenia murina used by Dujardin, is preoccupied, hav- 
ing been applied before 181:5 to another form, it can not be retained in 
this connection. Tsenia nana Siebold. 1852 being the next available 
name, the correct designation of the species, placed in its proper 
genus, is therefore IIymenoJep>is nana. 
Linstow (1896a) believed he found differences which would justify a 
specific distinction between the forms in man and in the rat, but, as 
Massari (1898) has pointed out, his results are not entireh’ free from 
criticism, and his arguments rather unconvincing. 
Ilyrnenolejyis nana may, accordingly, be regarded as occurring not 
only in man, but also in the rat, and in the two hosts showing slight 
and variable differences, brought about by the action upon the para- 
site of an environment somewhat different in the two cases. 
ANATOMICAL DESCRIPTION. 
EXTERNAL ANATOMY. 
As is well indicated by its name (nana. a dwarf) the worm under 
consideration is characterized preeminently by its small size (fig. 
5A). Being also very delicate, and likely to be broken in pieces, it 
is thus a difficult matter to discover specimens in the feces, unless 
passed in large numbers. 
Strobila. — Complete strobil^e with gravid segments ina\^ be found 
ranging in length from 5 or 6 mm. (Blanchard, 1891a) to a maximum, 
as recorded so far, in man of 35 mm. (Mertens, 1892). In the rat a 
length as great as 15 mm. has been observed (Stossich, 1898). 
Favarcq (1891a) found a worm 75 mm. long, in the intestine of the 
garden dormouse (Eliornys quercinns)^ which he believed to be a 
