i8i 
the portal vein to the bladder. Another very important question is 
why they do not remain in the veins of the rectum (or the intestine in 
general, which is apparently the original habitat of the Schistosomes), 
and how they find their way through the (comparatively) few connec¬ 
tions between rectal and vesical veins into the latter. In order to 
explain this remarkable ‘ knowledge of anatomy ’ I will draw attention 
to some well-known facts derived from the comparative biology of 
other parasitic worms. The larvae of the Filaria baucrofli, e.g., 
after having been sucked up by a mosquito, leave the intestine by 
perforating its wall, and make their way into the thoracic muscles ; the 
larvae of the Filaria immitis do tlie same, but seek the Malpighian 
tubes. The mature Ankylostoma worms do not live irregularly 
scattered throughout the small intestine, but chiefly accumulate in a 
certain region. Many Aniphistomes inhabit the first stomach of 
their hosts (Ruminants), but the specimens found there are. according 
to my personal experience, never below a certain size. The young 
stages live, often by hundreds, in the small intestine. They have 
been swallowed along with the food, but do not at once settle in the 
stomach (which they have to traverse In order to get to the 
small intestine); it is not until they have reached a certain size at 
this provisional habitat in the small intestine that they return to 
the first stomach which is their definite habitat. 
In all these cases the worms must be guided by something which 
makes them find their place of destination. I have no doubt that 
this something is given in the peculiar chemical composition of the 
organs, or the juices, at the respective places; in other words, the 
wanderings come under the phenomena of ‘ chemiotaxis. One 
might suppose that the conditions in the small intestine of man are 
about the same throughout its total length (at least behind the 
entrance of the bile ducts). But the fact that the Ankylostoma worms 
normally settle in the anterior half only, is to my mind evidence that 
there must be differences wliich to the worms are noticeable, and lead 
them to select one special place in preference to any other. The 
fact that stray specimens may often be found more or less far away 
from this place, does not shake the rule ; these specimens are the 
exceptions which strengthen the rule.’ 
Starting from these reflections t conclude that the Bilharzia worms, 
also, are guided in their journey by chemiotactic influences. I do 
