35 
ing from 4 to 14 }’ears, 20 cases of II. nana were found, and noticing 
the great similarity of the two forms, he was thus led to their identi- 
fication, as one and the same species, or at most as scarcel}" distinguish- 
able varieties of a single species. In view of the fact that, although 
IlymenoJepis nana was so exceedingly common in these regions, no 
corresponding c 3 ^sticercoid was to be found in the many animals exam- 
ined, belonging to species which a ]?riori might be considered possible 
intermediate hosts, Grassi then resorted to the idea of a direct develop- 
.ment; and, indeed, experiments along this line resulted in a demonstra- 
tion of the fact that the eggs of Hynienolejns nanalvom one rat when 
fed to another develop into mature worms in the intestine. Develop- 
ment, however, was found not to be direct, i. e., the embiyo from the 
egg did not grow immediate!}^ into the form of the adult, but pene- 
trating into a villus developed there into a c^^sticercoid, which in turn 
reentered the alimentary canal, to become transformed into the adult 
stage. The rat was thus shown to act not onlv as the definitive host, 
but also as the intermediate host. In spite of the evident exactness 
of the results of these experiments, and in spite of the probabilitv that 
the c}"sticercoid {Cercocystis fenebrionis) of the meal worm is more 
likely the intermediate stage of Tsenia microstoma.^ Leuckart (1887) 
still considered this c\^sticercoid the intermediate stage in the normal 
life cycle of Ilymenolepis murina nana).^ and looked upon the 
development of an intermediate stage in the villus of the rat’s intes- 
tine as unusual, and not of common occurrence in the natural order 
of things. The balance of evidence, however, seems to indicate 
that there is no connection between the above-named cysticercoid 
and Hymenolejyis nana^ but whether the eggs of the latter may not 
develop into a C}’sticercoid in some insect, as well as in the intestinal 
villi of the rat, is not known. So far as the direct evidence goes, 
however, the development as outlined b}^ Grassi must be considered 
the normal and usual method. 
The experiments by which the life histoiy was determined are as 
follows (Grassi, 188Th; Grassi & Rovelli, 1892a): 
Thirty-four white rats were used, aged from 1 to 3 months, kept in 
clean cages, closed, except on one side, which was covered with wire 
screen. After weaning, the rats were fed onh' with bread and pure 
water. The mothers were determined to be free from tapeworm, 
during lactation by examination of the feces, and afterwards bv kill- 
ing and examining post mortem. The experiments were repeated 11 
times, each time by feeding 1 to 3 of the 31 rats with mature segments 
of Ilymenolepis nana from infected rats and placing them in separate 
cages, and also at the same time isolating 1 or 2 which had not been 
thus fed, in order that there might be a check on the results. Con- 
stanth" among the former, Ilymenolepis nana developed in greater 
or less number, sometimes more than 100; among the latter no speci- 
mens whatever were found. 
