35 
ing‘ from 4 to 14 }'ears. 20 cases of II. iiana were found, and noticing 
the great similarity of the two forms, he was thus led to their identi- 
lication. as one and the same species, or at most as scarcely distinguish- 
able varieties of a single species. In view of the fact that, although 
Ilymenolejns nana was so exceedingly common in these regions, no 
corresponding cysticercoid was to be found in the many animals exam- 
ined, belonging to species which a i?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 Hymenolejns nana from 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 embryo from the 
egg did not grow immediately into the form of the adult, but pene- 
trating into a villus developed there into a cysticercoid, which in turn 
reentered the alimentarv canal, to become transformed into the adult 
stage. The rat was thus shown to act not only 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 probability that 
the cysticercoid {Cercocystls tenehrionis) of the meal worm i§ more 
lik-elv the intermediate stage of Txnia mi<^rostorna^ Leuckart (18ST) 
still considered this cvsticercoid the intermediate stage in the normal 
life cycle of Ilyrnenolej)^ niurina {=H. 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 Hymenolejns 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 by Grassi must be considered 
the normal and usual method. 
The experiments by which the life history 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 only with bread and pure 
water. The mothers were determined to be free from tapeworm, 
during lactation b}^ examination of the feces, and afterwards by kill- 
ing and examining post mortem. The experiments were repeated 11 
times, each time by feeding 1 to 3 of the 34 rats with mature segments 
of Hyrnenolejyis 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- 
stantly among the former, Hymenolejns developed in greater 
or less number, sometimes more than 100; among the latter no speci- 
mens whatever were found. 
