18 H. B. FANTHAM. 
come to a dead stop or just as suddenly proceed more slowly. 
It is a matter of indifference which end of the body is directed 
forwards, for the parasite is capable of suddenly reversing 
its direction of movement and returning on its own path, 
apparently in an almost exact straight line or circle. I do 
not consider this retracing of its path to be due to unfavour- 
able environment, as suggested by Novy in the case of 
S. obermeiert, for I have observed it constantly taking place 
inside the crystalline style. The organism can then travel 
with or against the current indifferently. A very great deal 
of energy seems to be used in the motion of the organism. 
The body of the parasite can be distinguished during motion 
in the case of 8. balbianii with some difficulty, but some- 
times S. anodontz moves too rapidly for its outline to be 
discernible. However, in the case of 8S. balbian1ui, I do not 
agree with Perrin when he remarks: “ When liberated from 
the crystalline style into sea water, motion is very fast, .. . 
The body itself cannot be seen. ‘Two black points, the 
anterior and posterior ends of the animal are alone visible.” 
When moving in this manner, which, I take it, is in a plane 
approximately that of the preparation and along the stage of 
the microscope, I was always able to see the outline of the 
body, however fast the organism moved. A somewhat blurred 
appearance might occasionally arise, even in the “ side-to- 
side” movement of the whole body, quoted by Perrin, but 
even then the organism, as a whole, was visible. The ends 
in ordinary progression do not lie in a.different plane from 
that of the intermediate parts of the body, nor do they appear 
to be especially fixed, for if one end seems somewhat fixed 
the other one often moves from side to side. In rapid for- 
ward motion, then, the body seems to be thrown into undu- 
lations travelling down the body from the anteriorly directed 
end to the posterior one, while the body rotates on itself in a 
spiral manner, and the side-to-side movements or lashing of 
one end are reduced to a minimum at this time. 
Sometimes the organism appears suddenly from a deeper 
level of the hquid under examination and swims, or rather, 
