F. W. Flattely 
269 
In addition to Moniezia , Stiles recognises two related genera of tape¬ 
worms as having representatives in cattle, sheep and allied animals, viz. the 
genus Thysanosoma (Diesing, 1834) and Stilesia (Railliet, 1893), neither of 
which has so far come under my notice in Britain. 
It is remarkable that notwithstanding the wide distribution of the various 
species of Moniezia and the commonness of their occurrence, the life-history 
has not in any single instance been worked out. The same is true of the other 
two genera of tapeworms found in herbivorous animals, viz. Thysanosoma and 
Stilesia. Doubtless our ignorance is to be attributed rather to lack of investi¬ 
gation than to anything inherently peculiar in the development of these forms, 
attention, naturally enough, having been focussed mainly upon the species 
directly affecting man or coming more closely under his notice. From an 
economic point of view alone, however, the life-history of Moniezia tapeworms 
deserves the closest attention, since the total loss to the country, owing to 
depreciation in the value of the lambs affected by these parasites, must be 
considerable. 
Suggestions which have been put forward hitherto as to the life-history 
of Moniezia have been made from two distinct view-points. Either they 
require an intermediate stage in the body of some invertebrate animal or they 
assume that the adult tapeworm may develop directly from the egg without 
change of host. The first view is the one most generally held since it accords 
with our knowledge of the great majority of other tapeworm histories. The 
latter view has been supported principally by Megnin and Curtice and, in 
spite of its apparent improbability, should not be hastily rejected. It has been 
opposed by Moniez (1879) and Railliet (1880) among others, the former, how¬ 
ever, not altogether excluding the possibility of a direct development in the 
one host. Experience shows that it is rash to dogmatise about tapeworm 
life-histories. Grassi, for instance, in 1889, was able to infect mice with Taenia 
murina by feeding them on the eggs, the cysticercoid stage appearing in 3-4 
days in the intestinal villi and the adult Taenia in 15-30 days. Recently a 
case came under my own notice of a soldier who had developed literally scores 
of cysticercoids of Taenia solium as a result of having accidentally ingested 
the eggs of this form (see Hughes, 1921). On the other hand, attempts made 
by Curtice, Stiles and recently by the writer to produce direct infection have 
all been fruitless. The thought suggests itself, however, that before finally 
rejecting the direct infection theory, as supported by Megnin and Curtice, 
it would perhaps be advisable to determine whether some form of maturation 
is not necessary before the eggs will develop. In natural conditions the pro- 
glottids would hardly ever be ingested immediately they are dropped. They 
would probably lie about in the faeces or on the grass for some time. 
Another consideration presents itself with regard to this question of direct 
infection, viz. the multiplicity of closely related species affecting the same host. 
Are we to regard this as evidence against the direct infection theory? One feels 
tempted to do so and to associate each particular species of Moniezia with 
Parasitology xiv 
18 
