MICROSCOPIC ORGANISMS IN INTESTINAL CANAL, 255 
Ameebe, sporoid cells, and zoospores really constitute stages in 
one cycle of development, more especially when certain observa- 
tions, an account of which will be met with farther on, are taken 
into account. Any direct origin of Amcebe, from characteristic 
sporoid cells in human excreta, does not seem to take place. 
Allowing, then, in the meantime, that the characteristic zoo- 
spores, Amcebze, and sporoid cells occurring as parasites within 
the human digestive canal are all members of the developmental 
cycle of one specific organism, how can we account for the 
extreme frequency with which they are present? ‘Taking the 
very great susceptibility of the organisms to the influence of ex- 
ternal conditions, and the fact that the media in which they 
escape from the body seem, as a rule, to undergo changes cer- 
tainly fatal to them, it appears at first sight very difficult to do 
so satisfactorily. We might, indeed, take refuge in the suppo- 
sition that, after the germs have once obtained an entrance, they 
remain persistently within the body, giving rise to constantly 
recurring generations of the parasite, but such an hypothesis is 
hardly consistent with the fact that in the case of a given indi- 
vidual they may appear suddenly after considerable intervals of 
apparently entire absence, and after persisting for varying periods 
may again vanish, only to reappear as before at a later period. 
We should, therefore, be compelled farther to assume that 
periodical retentions, either of the germs or of the developed 
organisms, take place somewhere within the body, and alternate 
with uncertain periods of discharge, or that their appearance and 
disappearance from the excreta is determined solely by conditions 
in the latter allowing or preventing their persistence in the 
contents of the lower portion of the digestive canal. 
While allowing the possibility of such explanations, I do not 
regard them as correct, but believe that the appearance and dis- 
appearance of the parasitic forms are due to the successive in- 
troduction of extraneous elements and the subsequent discharge 
of the result of their development. It is as difficult to give a 
definite opinion as to the precise source of these organisms as it 
is to state whence the oidial and bacterial elements of the intes- 
tinal contents are derived. They are, as has already been pointed 
out, almost constantly present in varying numbers in the intes- 
tinal canal, and are in all probability introduced with ingesta of 
various kinds, 
Il. The Intestinal Monads and Amebe of Cows and Horses. 
It is now more than five years since, whilst studying the 
development of Pilobolus crystallinus, I first encountered what 
it appears may be regarded as the perfect fructifying or repro- 
