I have said above that, a priori, a great structural similarity of tht 
adult stages would not necessarily be a proof of there being only one 
species. If, on the other hand, I am asked to acknowledge a specific 
difference between ScA. hcematobiuni and Sch. mansoni, in spite 
of their great internal resemblance, I certainly expect that the 
other proofs in favour of the existence of a separate species riD 
be absolutely clear and stringent. We will now see how these parts 
of Dr. Samson’s evidence stand an earnest scientific test. 
There are numerous cases wliere closely allied parasites (of man 
or animals) show marked differences with regard to their special 
habitat in the body of their host; the lesions they produce will then 
show a peculiar localisation. Closely allied species may further 
differ in their geographical distribution w'hich is indicated by the 
geographical occurrence of the respective lesions. It is, therefore, 
tlUU IIIC • — 
valuable 
a priori, imaginable that the localisation anu me gcu 
occurrence of certain symptoms may in certain cases be a va 
support for the distinction of the species which cause them. A 
different question is whether variations observed in the localisation 
and the geographical distribution of certain symptoms may be used 
as proof that they are due to different species of parasites, k 
this connection I must point out that, quite generally speaking, 
observations of the alleged sort are, in principle, statistical 
I do not underestimate the value which statistical observations mav 
ave under various circumstances ; but it is a fact also that from the 
same statistics more or less opposite conclusions maybe 
7 ” according to tlie point of view from which they are looked at 
^ ^ statistics themselves are by no means all of them 
qua y reliable. On the whole, therefore, I think that it wiU always 
^ ^*^f>stical observations very carefully before con- 
An ^ sliow, as an objective proof of some theon' 
discussprt t" of the truth of what has just been said will be 
discussed towards the end of this article. 
statistical^oh^^^. present occupies us Dr. SambON uses 
distribution oTcertl'irw^''"”^ “"I 
a species nF ■' additional proofs of the existence of 
when the as established, notwithstanding. 
' 'onal proofs were binding and did not leave uu) 
