42 
SOME PHENOMENA ASSOCIATED WITH 
PARASITISM. 
By F. A. POTTS, M.A. 
Fellow of Trinity Hall , Cambridge. 
(Three Figures.) 
Introduction. 
Observation on the behaviour of animals infected by parasites 
has generally been confined to direct effects, and .such as mainly 
concern the invaded parts. It has of course often been shown that 
the constitution of the blood (at least with regard to its cellular 
elements) is altered in most kinds of parasitic affections even when 
a gut-parasite is in question. This indication of the indirect action 
of parasites leads to the consideration of cases like those below where 
the influence of the invading organism exerted through the medium 
of the blood results in definite changes of the reproductive system. 
Probably no other part of the organism responds in so marked a manner 
to the readjustment of the general metabolism which the parasite 
occasions, but there is still great possibility that changes of consider¬ 
able interest may take place in other parts of the body. 
I. Changes in the Reproductive System of the Host. 
It is a common experience for an observer of marine nature to find, 
tucked under the abdomen of a crab, a yellow globular body which 
with its connected root system ramifying through the body of the host, 
has more the appearance of a pathological growth than a separate 
organism. It has however been known for more than seventy years 
that this curious parasite, to which the name Sacculina was given, is 
an aberrant cirripede. The curious nature of its life-history has 
