in the digenetic Treniatodes. I have acted according to this 
principle in formulating m\- theory. As n matter of course, in doii^ 
this, I depend upon our present knowledge. It often happnis tbit 
a theory which seems probable and natural at one time isatanolbe 
upset by new facts which, though not annihilating the older lads, 
yet make them appear in a different light. I cannot foretell it 
present what facts may be in store for us with regard to Bilharzioss 
and, therefore, cannot say that the theory which I defend at present 
is the right one in every detail. But I think that I can claim 
that it is based upon a large number of anatomo^pathological aod 
helminthological facts deliberately weighed and compared. I have 
thought these remarks necessary in the face of Dr. SaMBON's allnacn 
that myself, and all the other workers in Egypt, have not been aWe 
within long years to find the solution of a problem which acewding 
to him was easy enough after all. 
So as to be quite impersonal I will myself draw attention to ai 
important biological point which 1 am not yet able to safBcienii) 
account for. I am convinced that the lateral-spined an 
abnormal and, probably, unfertilized. Nevertheless, when they appeal 
in the faeces they very often contain a fully-developed miracidium 
If we suppose, with some earlier authors, that mature females are 
undei certain circumstances, still capable of producing sud 
lateral spined eggs, the dilemma would resolve itself into tk 
quesUon as to vv hat these conditions arc (spontaneous con¬ 
traction , pressure of the surrounding organs, either accidental oi 
owmg to their movements ; 8cc). 1 have already said that this porn! 
js not yet determined. To me it seems, on the whole, very 
lat probable, that fully mature females continue to produce 
m true, the presence of the roiracidia 
narHif- eggs arc capable of developing ^1' 
ditir From what has been obsen-ed in the hennaphn> 
ordpi-f a appears that the eggs must be fertilized, in 
Trema^ ^ pnori. one ought to expect the same also m dif 
takabt h"' J However, considering the unin .5 
the preservatin^^^f^? connected with this separation in regard to 
w'hich the c; h " ° ^ ^ under the peculiar circumstances under 
cor^ti at f ‘--ing. and considering further the very 
complicated development of many Trematode.s in Jhich often 
